Ankle Taping Does Not Impair Performance in Jump or Balance Tests

This study aimed to investigate the influence of prophylactic ankle taping on two balance tests (static and dynamic balance) and one jump test, in the push off and the landing phase. Fifteen active young subjects (age: 21.0 ± 4.4 years) without previous ankle injuries volunteered for the study. Each participant performed three tests in two different situations: with taping and without taping. The tests were a counter movement jump, static balance, and a dynamic posturography test. The tests and conditions were randomly performed. The path of the center of pressures was measured in the balance tests, and the vertical ground reaction forces were recorded during the push-off and landing phases of the counter movement jump. Ankle taping had no influence on balance performance or in the push off phase of the jump. However, the second peak vertical force value during the landing phase of the jump was 12% greater with ankle taping (0.66 BW, 95% CI -0.64 to 1.96). The use of prophylactic ankle taping had no influence on the balance or jump performance of healthy young subjects. In contrast, the taped ankle increased the second peak vertical force value, which could be related to a greater risk of injury produced by the accumulation of repeated impacts in sports where jumps are frequently performed.

Key points

• Ankle taping has no influence on balance performance.
• Ankle taping does not impair performance during the push-off phase of the jump.
• Ankle taping could increase the risk of injury during landings by increasing peak forces.

Key words: Biomechanics, propioception, force platform, ground reaction forces, center of pressure     

Acute Effects of Two Different Warm-Up Protocols on Flexibility and Lower Limb Explosive Performance in Male and Female High Level Athletes

This study examined the effects of two different warm-up protocols on lower limb power and flexibility in high level athletes. Twenty international level fencers (10 males and 10 females) performed two warm-up protocols that included 5-min light jogging and either short (15s) or long (45s) static stretching exercises for each of the main leg muscle groups (quadriceps, hamstrings and triceps surae), followed by either 3 sets of 3 (short stretching treatment), or 3 sets of 5 tuck jumps (long stretching treatment), in a randomized crossover design with one week between treatments. Hip joint flexion was measured with a Lafayette goniometer before and after the 5-min warm-up, after stretching and 8 min after the tuck jumps, while counter movement jump (CMJ) performance was evaluated by an Ergojump contact platform, before and after the stretching treatment, as well as immediately after and 8 minutes after the tuck jumps. Three way ANOVA (condition, time, gender) revealed significant time (p < 0.001) and gender (p < 0.001) main effects for hip joint flexion, with no interaction between factors. Flexibility increased by 6. 8 ± 1.1% (p < 0.01) after warm-up and by another 5.8 ± 1.6% (p < 0.01) after stretching, while it remained increased 8 min after the tuck jumps. Women had greater ROM compared with men at all time points (125 ± 8° vs. 94 ± 4° p<0.01 at baseline), but the pattern of change in hip flexibility was not different between genders. CMJ performance was greater in men compared with women at all time points (38.2 ± 1.9 cm vs. 29.8 ± 1.2 cm p < 0.01 at baseline), but the percentage of change CMJ performance was not different between genders. CMJ performance remained unchanged throughout the short stretching protocol, while it decreased by 5.5 ± 0.9% (p < 0.01) after stretching in the long stretching protocol However, 8 min after the tuck jumps, CMJ performance was not different from the baseline value (p = 0.075). In conclusion, lower limb power may be decreased after long periods of stretching, but performance of explosive exercises may reverse this phenomenon.

Key points

• Stretching of the main leg muscle groups for 45 s results in a relatively large decrease (by 5.5%) in subsequent jumping performance
• Stretching of the main leg muscle groups for only 15 s results in an increase in flexibility similar to that of the longer duration stretching (by 12.6%), with no change in subsequent jumping performance
• Performance of a PAP exercise such as tuck jumps may reverse the negative effects of long duration stretching on leg muscle power. However, jumping performance is not increased above baseline
• Speed/power athletes should be advised against using long duration stretching. The number of repetitions of a PAP exercise such as the tuck jumps, should be further examined in order to induce an increase in explosive performance during competition

Key words: Countermovement jump, stretching, post-activation potentiation, fencing     

Effects of Electrostimulation and Plyometric Training Program Combination on Jump Height in Teenage Athletes

The purpose of this study was to examine the effects of eight-week (2 days/week) training periods of plyometric exercises (PT) and neuromuscular electrostimulation (EMS) on jump height in young athletes. Squat jump (SJ), counter movement jump (CMJ) and drop jump (DJ) were performed to assess the effects of the training protocols 98 athletes (100 & 200m and 100m & 110m hurdles) voluntarily took part in this study, 51 males (52%) and 47 females (48%), 17.91 ± 1.42 years old, and 5.16 ± 2.56 years of training experience. The participants were randomly assigned to four different groups according to the frequency and the timing of the stimulation. Analysis of covariance was used to analyze the effects of every training program on jump height. Our findings suggest that compared to control (Plyometrics (PT) only), the combination of 150Hz EMS + PT simultaneously combined in an 8 week (2days/week) training program, we could observe significant jump height improvements in the different types of strength: explosive, explosive-elastic, and explosive-elastic-reactive. The combination of PT after ≤ 85 Hz EMS did not show any jump height significant increase in sprinters. In conclusion, an eight week training program (with just two days per week) of EMS combined with plyometric exercises has proven useful for the improvement of every kind of vertical jump ability required for sprint and hurdles disciplines in teenage athletes.

Key points

• The combined use of high frequency electromyostimulation and plyometric training 2 days/week in an 8 week training program produce significant improvements in jump height in teenage athletes.
• A high-frequency (≥ 150 Hz) EMS and its simultaneous application with PT can significantly contribute to the improvement of the three different types of strength manifestations (explosive, explosive-elastic and explosive-elastic-reactive strength).
• An alternate training with different stimulation frequencies [85Hz EMS/ PT combination and 150Hz EMS + PT simultaneous combination] only has significant improvement effects in SJ.
• The combination of PT after ≤ 85 Hz EMS did not show any jump height significant increase in teenage athletes.
• The timing of EMS and PT application during training must be taken into account according to the type of jump.

Key words: Jump height, squat jump, counter movement jump, drop jump, combined training     

Reliability and Validity of a Wireless Microelectromechanicals Based System (Keimove?) for Measuring Vertical Jumping Performance

The aim of this study was to determine the validity and reliability of a microelectromechanicals (MEMs) based system (Keimove™) in measuring flight time and takeoff velocity during a counter-movement jump (CMJ). As criterion reference, data of a high- speed camera (HSC) and a force-platform (FP) synchronized with a linear position transducer (LPT) was used. Thirty professional soccer players completely familiarized with the CMJ technique performed three CMJs. The second and third trials were used for further analysis. The Keimove™ system, the HSC and the FP synchronized with the LPT (FP+LPT) simultaneously measured the CMJ performance. During each repetition, the Keimove™ system registered flight time and velocity at takeoff. At the same time and as criterion reference, both the HSC and the FP recorded the flight time while the LPT+FP registered the velocity at takeoff. Pearson correlation coefficients for the flight time were high (r = 0.99; p < 0.001) when Keimove™ system was compared with the HSC or the FP+LPT, respectively. For the velocity at takeoff variable, the Pearson r between the Keimove™ system and the FP+LPT was lower although significant at the 0.05 level. No significant differences in mean values were observed for flight times and velocity at takeoff between the three devices. Intraclass correlations and coefficients of variation between trials were similar and ranged between 0.92-0.97 and 2.1-7.4, respectively. In conclusion, the Keimove™ system represents a valid and reliable instrument to measure velocity at takeoff and flight time during CMJ testing. Thus, this MEMs-based system will offer a portable, cost-effective tool for the assessment CMJ performance.

Key points

• The Keimove™ system is composed of specific software and a wireless MEMs-based device designed to be attached at the lumbar region of the athlete.
• The Keimove™ system is a mechanically valid and reliable instrument in measuring flight time and velocity at takeoff during CMJ.
• The validity of the Keimove™ system was determined by comparing its mean flight time and velocity at takeoff with data obtained simultaneously with both a high-speed camera and a force platform synchronized with a linear position transducer.

Key words: Counter-movement jump, microelectromechanical systems, testing     

Pre-Activity Modulation of Lower Extremity Muscles Within Different Types and Heights of Deep Jump

The purpose of this study was to determine modulation of pre- activity related to different types and heights of deep jump. Sixteen male soccer players without experience in deep jumps training (the national competition; 15.0 ± 0.5yrs; weight 61.9 ± 6.1kg; height 1.77 ± 0.07m), who participated in the study, performed three types of deep jump (bounce landing, counter landing, and bounce drop jump) from three different heights (40cm, 60cm, and 80cm). Surface EMG device (1000Hz) was used to estimate muscle activity (maximal amplitude of EMG - A_maxEMG; integral EMG signal - iEMG) of five muscles (mm.gastrocnemii, m.soleus, m.tibialis anterior, m.vastus lateralis) within 150ms before touchdown. All the muscles, except m. gastrocnemius medialis, showed systematic increase in pre-activity when platform height was raised. For most of the lower extremity muscles, the most significant differences were between values of pre-activity obtained for 40 cm and 80 cm platforms. While the amount of muscle pre-activity in deep jumps from the heights above and beneath the optimal one did not differ significantly from that generated in deep jumps from the optimal drop height of 60 cm, the patterns of muscle pre-activity obtained for the heights above the optimal one did differ from those obtained for the optimal drop height. That suggests that deep jumps from the heights above the optimal one do not seem to be an adequate exercise for adjusting muscle activity for the impact. Muscle pre-activity in bounce drop jumps differed significantly from that in counter landing and bounce landing respectively, which should indicate that a higher amount of pre-activity generated during bounce drop jumps was used for performing take-offs. As this study included the subjects who were not familiar with deep jumps training, the prospective studies should reveal the results of athletes with previous experience.

Key points

• Height factor proved to be more relevant for the change in pre-activation level compared to the drop jump type factor.
• There is evident qualitative difference in pattern of pre-activation from lower and higher drop heights, compared to pattern of pre-activation obtained from optimal drop height.
• Drop jumps from the heights above the optimal one are not adequate for nicely preparing muscle activity for the impact.

Key words: Electromyography, programmed muscle activity, landings, drop jumps     

Effects of Baseline Levels of Flexibility and Vertical Jump Ability on Performance Following Different Volumes of Static Stretching and Potentiating Exercises in Elite Gymnasts

This study examined the effects of baseline flexibility and vertical jump ability on straight leg raise range of motion (ROM) and counter-movement jump performance (CMJ) following different volumes of stretching and potentiating exercises. ROM and CMJ were measured after two different warm-up protocols involving static stretching and potentiating exercises. Three groups of elite athletes (10 male, 14 female artistic gymnasts and 10 female rhythmic gymnasts) varying greatly in ROM and CMJ, performed two warm-up routines. One warm-up included short (15 s) static stretching followed by 5 tuck jumps, while the other included long static stretching (30 s) followed by 3x5 tuck jumps. ROM and CMJ were measured before, during and for 12 min after the two warm-up routines. Three-way ANOVA showed large differences between the three groups in baseline ROM and CMJ performance. A type of warm-up x time interaction was found for both ROM (p = 0.031) and CMJ (p = 0.016). However, all athletes, irrespective of group, responded in a similar fashion to the different warm-up protocols for both ROM and CMJ, as indicated from the lack of significant interactions for group (condition x group, time x group or condition x time x group). In the short warm-up protocol, ROM was not affected by stretching, while in the long warm-up protocol ROM increased by 5.9% ± 0.7% (p = 0.001) after stretching. Similarly, CMJ remained unchanged after the short warm-up protocol, but increased by 4.6 ± 0.9% (p = 0.012) 4 min after the long warm- up protocol, despite the increased ROM. It is concluded that the initial levels of flexibility and CMJ performance do not alter the responses of elite gymnasts to warm-up protocols differing in stretching and potentiating exercise volumes. Furthermore, 3 sets of 5 tuck jumps result in a relatively large increase in CMJ performance despite an increase in flexibility in these highly-trained athletes.

Key Points

• The initial levels of flexibility and vertical jump ability have no effect on straight leg raise range of motion (ROM) and counter-movement jump performance (CMJ) of elite gymnasts following warm-up protocols differing in stretching and potentiating exercise volumes
• Stretching of the main leg muscle groups for only 15 s has no effect on ROM of elite gymnasts
• In these highly-trained athletes, one set of 5 tuck jumps during warm-up is not adequate to increase CMJ performance, while 3 sets of 5 tuck jumps result in a relatively large increase in CMJ performance (by 4.6% above baseline), despite a 5.9% increase in flexibility due to the 30 s stretching exercises

Key Words: Gymnastics, countermovement jump, stretching, post- activation potentiation     

The effect of mild symptomatic patellar tendinopathy on the quadriceps contractions and the Fente motion in elite fencers

To investigate how mild symptomatic patellar tendinopathy (PT) affects quadriceps contractions and the Fente motion, this case-control study examined elite fencers who continue to train and play fully with mild tendon pains. Twenty-four elite fencers (10 women) with mild symptomatic PT and 24 controls (10 women) participated in the study. Concentric/eccentric isokinetic strength of the quadriceps was tested, and peak torque and total work were recorded. Kinematic data from the knee during the Fente motion were collected. The first analysis period (P1) was after heel contact to the maximal flexion of the knee, and the second (P2) was right after P1 to heel-off. Normalized peak torque and work of concentric/eccentric contractions were not significantly different. Affected fencers demonstrated significantly reduced angular velocities at P2 (p = 0.042). The male fencers did not demonstrate any differences. The affected female fencers demonstrated significantly weaker concentric peak torque at 60°·s^-1 (p = 0. 009) and 180°·s^-1 (p = 0.047) and less concentric work at 60°·s^-1 (p = 0.020). They also demonstrated significantly reduced average angular velocities at P2 (p = 0.001). Therefore, mild symptomatic PT seems to have an effect on the isokinetic concentric contraction of the quadriceps and the angular velocity of the knee during the backward Fente motion in elite female fencers who are participating fully in training and competition.

Key points

• It is likely that even mild symptomatic patellar tendinopathy could affect the athletic performances in elite fencers.
• Elite female fencers are more likely to be affected substantially by symptomatic patellar tendinopathy in their sporting ability than male fencers.
• Because weak concentric knee extensors may affect the performance in fencing, not only eccentric training for symptomatic patellar tendinopathy but also proper concentric training of the quadriceps may be helpful in a rehabilitation program of elite female fencers who are participating fully in their training and competition.

Key words: Patellar tendinopathy, elite fencers, isokinetic, kinematics     

The Effect of Gender and Fatigue on the Biomechanics of Bilateral Landings from a Jump: Peak Values

Female athletes are substantially more susceptible than males to suffer acute non-contact anterior cruciate ligament injury. A limited number of studies have identified possible biomechanical risk factors that differ between genders. The effect of fatigue on the biomechanics of landing has also been inadequately investigated. The objective of the study was to examine the effect of gender and fatigue on peak values of biomechanical variables during landing from a jump. Thirty-two recreational athletes performed bilateral drop jump landings from a 40 cm platform. Kinetic, kinematic and electromyographic data were collected before and after a functional fatigue protocol. Females landed with 9° greater peak knee valgus (p = 0.001) and 140% greater maximum vertical ground reaction forces (p = 0.003) normalized to body weight compared to males. Fatigue increased peak foot abduction by 1.7° (p = 0.042), peak rectus femoris activity by 27% (p = 0.018), and peak vertical ground reaction force (p = 0.038) by 20%. The results of the study suggest that landing with increased peak knee valgus and vertical ground reaction force may contribute to increased risk for knee injury in females. Fatigue caused significant but small changes on some biomechanical variables. Anterior cruciate ligament injury prevention programs should focus on implementing strategies to effectively teach females to control knee valgus and ground reaction force.

Key points

• Female athletes landed with increased knee valgus and VGRF which may predispose them to ACL injury.
• Fatigue elicited a similar response in male and female athletes.
• The effectiveness of sports injury prevention programs may improve by focusing on teaching females to land softer and with less knee valgus.

Key words: Anterior cruciate ligament injury, injury prevention, knee injury, sports biomechanics     

Jump Kinetic Determinants of Sprint Acceleration Performance from Starting Blocks in Male Sprinters

The purpose of this research was to identify the jump kinetic determinants of sprint acceleration performance from a block start. Ten male (mean ± SD: age 20 ± 3 years; height 1.82 ± 0.06 m; weight 76.7 ± 7.9 kg; 100 m personal best: 10.87 + 0.36 s {10.37 - 11.42}) track sprinters at a national and regional competitive level performed 10 m sprints from a block start. Anthropometric dimensions along with squat jump (SJ), countermovement jump (CMJ), continuous straight legged jump (SLJ), single leg hop for distance, and single leg triple hop for distance measures of power were also tested. Stepwise multiple regression analysis identified CMJ average power (W/kg) as a predictor of 10 m sprint performance from a block start (r = 0.79, r² = 0.63, p<0.01, SEE = 0.04 (s), %SEE = 2.0). Pearson correlation analysis revealed CMJ force and power (r = -0.70 to -0.79; p = 0.011 - 0.035) and SJ power (r = -0.72 to -0.73; p = 0.026 - 0.028) generating capabilities to be strongly related to sprint performance. Further linear regression analysis predicted an increase in CMJ average and peak take-off power of 1 W/kg (3% & 1.5% respectively) to both result in a decrease of 0.01 s (0.5%) in 10 m sprint performance. Further, an increase in SJ average and peak take-off power of 1 W/kg (3.5% & 1.5% respectively) was predicted to result in a 0.01 s (0.5%) reduction in 10 m sprint time. The results of this study seem to suggest that the ability to generate power both elastically during a CMJ and concentrically during a SJ to be good indicators of predicting sprint performance over 10 m from a block start.

Key Points

• The relative explosive ability of the hip and knee extensors during a countermovement jump can predict 10 m sprint performance from a block start.
• The relative power outputs of male competitive sprinters during a squat jump can predict 10 m sprint performance from a block start.

Key words: Anthropometry, horizontal jumps, sprint performance, vertical jumps     

Effects of the Tennis Tournament on Players’ Physical Performance,Hormonal Responses,Muscle Damage and Recovery

The purpose of this study was to examine changes in selected physiological and performance variables of male tennis players (n=8) during a 3-day tennis tournament and the following 2-day recovery period. Each player played three two-hour tennis matches. The following measurements were taken: blood samples for serum testosterone T, cortisol C, creatinekinase CK, performance tests of maximal isometric leg press MVC and maximal rate of force development RFD, 5m run 5m, 5-leap 5l, counter movement jump CMJ and serve velocity S and DOMS questionnaire. During the games at 40 and 80 minutes the following tests were made: blood sample, MVC, 5m, CMJ and S. Both MVC and RFD were before the 2^nd and 3^rd match significantly lower than before the 1^st match (p < 0.02) and remained reduced after 1 to 2 days of recovery. Serum C was significantly higher than the baseline value before each match (p < 0.05) and after 40 minutes of playing (p < 0.03). Serum T elevated from the baseline during every match at T40 (p < 0.02). CK elevated during the whole tournament peaking after the 3rd match. After one rest day CK was still significantly higher than the baseline value. Upper and lower body DOMS were elevated significantly but remained above the baseline after one rest day. The tennis tournament leads to reduced MVC and RFD, increased muscle damage and soreness and reduced recovery. It seems that a tennis tournament causes such a heavy speed strength load for the legs in addition to muscle damage that the recovery of explosive attributes of leg extensor muscles is impaired after two days of rest after the tournament. Serum cortisol and testosterone concentration elevated before and during the tennis match, but the outcome of the tennis match is difficult to predict using C or/and T levels before, during or after the match.

Key Points

• The tennis tournament impairs player’s MVC and RFD, increases muscle damage and soreness and reduces recovery.
• One day of rest after the tennis tournament is insufficient to recover explosive attributes of leg extensor muscles.
• Serum cortisol and testosterone concentration elevated before and during tennis match.
• The result of the tennis match is difficult to predict using cortisol or/and testosterone levels before, during or after the match.

Key words: Tennis, maximal voluntary contraction, rate of force development, creatinekinase, fatigue     

Analysis of the Vertical Ground Reaction Forces and Temporal Factors in the Landing Phase of a Countermovement Jump

In most common bilateral landings of vertical jumps, there are two peak forces (F1 and F2) in the force-time curve. The combination of these peak forces and the high frequency of jumps during sports produce a large amount of stress in the joints of the lower limbs which can be determinant of injury. The aim of this study was to find possible relationships between the jump height and F1 and F2, between F1 and F2 themselves, and between F1, F2, the time they appear (T1 and T2, respectively) and the length of the impact absorption phase (T). Thirty semi-professional football players made five countermovement jumps and the highest jump of each player was analyzed. They were instructed to perform the jumps with maximum effort and to land first with the balls of their feet and then with their heels. All the data were collected using a Kistler Quattro Jump force plate with a sample rate of 500 Hz. Quattro Jump Software, v.1.0.9.0., was used. There was neither significant correlation between T1 and F1 nor between T1 and F2. There was a significant positive correlation between flight height (FH) and F1 (r = 0.584, p = 0.01) but no significant correlation between FH and F2. A significant positive correlation between F1 and T2 (r = 0.418, p < 0.05) and a significant negative correlation between F2 and T2 (r = -0.406, p < 0.05) were also found. There is a significant negative correlation between T2 and T (r = -0. 443, p < 0.05). T1 has a little effect in the impact absorption process. F1 increases with increasing T2 but F2 decreases with increasing T2. Besides, increasing T2, with the objective of decreasing F2, makes the whole impact absorption shorter and the jump landing faster.

Key points

• In the landing phase of a jump there are always sev-eral peak forces. The combination of these peaks forces and the high frequency of jumps during sports produces a large amount of stress in the joints of the lower limbs which can be determinant of injury.
• In the most common two-footed landings usually appear two peak forces (F1 and F2) in the force-time curve and the second one is usually related to injury’s risk. In this article it is shown that increasing the time F2 appears decrease F2.
• Increasing landing times could be counterproductive with respect to the goals of the sport. In this article it is shown that increasing the time F2 appears makes, however, the whole impact absorption shorter in du-ration.

Key words: Impact absorption, peak forces, vertical jump, injuries     

Ground Reaction Forces and Loading Rates Associated with Parkour and Traditional Drop Landing Techniques

Due to the relative infancy of Parkour there is currently a lack of empirical evidence on which to base specific technique instruction upon. The purpose of this study was to compare the ground reaction forces and loading rates involved in two Parkour landing techniques encouraged by local Parkour instructors and a traditional landing technique recommended in the literature. Ten male participants performed three different drop landing techniques (Parkour precision, Parkour roll, and traditional) onto a force plate. Compared to the traditional technique the Parkour precision technique demonstrated significantly less maximal vertical landing force (38%, p < 0.01, ES = 1.76) and landing loading rate (54%, p < 0.01, ES = 1.22). Similarly, less maximal vertical landing force (43%, p < 0.01, ES = 2.04) and landing loading rate (63%, p < 0.01, ES = 1.54) were observed in the Parkour roll technique compared to the traditional technique. It is unclear whether or not the Parkour precision technique produced lower landing forces and loading rates than the Parkour roll technique as no significant differences were found. The landing techniques encouraged by local Parkour instructors such as the precision and roll appear to be more appropriate for Parkour practitioners to perform than a traditional landing technique due to the lower landing forces and loading rates experienced.

Key points

• Parkour precision and Parkour roll landings were found to be safer than a traditional landing technique, resulting in lower maximal vertical forces, slower times to maximal vertical force and ultimately lesser loading rates.
• Parkour roll may be more appropriate (safer) to utilize than the Parkour precision during Parkour landing scenarios.
• The Parkour landing techniques investigated n this study may be beneficial for landing by non-Parkour practitioners in everyday life.

Key words: Kinetics, absorption, forefoot, roll.     

Reliability and Validity of the Polar V800 Sports Watch for Estimating Vertical Jump Height

This study aimed to assess the reliability and validity of the Polar V800 to measure vertical jump height. Twenty-two physically active healthy men (age: 22.89 ± 4.23 years; body mass: 70.74 ± 8.04 kg; height: 1.74 ± 0.76 m) were recruited for the study. The reliability was evaluated by comparing measurements acquired by the Polar V800 in two identical testing sessions one week apart. Validity was assessed by comparing measurements simultaneously obtained using a force platform (gold standard), high-speed camera and the Polar V800 during squat jump (SJ) and countermovement jump (CMJ) tests. In the test-retest reliability, high intraclass correlation coefficients (ICCs) were observed (mean: 0.90, SJ and CMJ) in the Polar V800. There was no significant systematic bias ± random errors (p > 0.05) between test-retest. Low coefficients of variation (<5%) were detected in both jumps in the Polar V800. In the validity assessment, similar jump height was detected among devices (p > 0.05). There was almost perfect agreement between the Polar V800 compared to a force platform for the SJ and CMJ tests (Mean ICCs = 0.95; no systematic bias ± random errors in SJ mean: -0.38 ± 2.10 cm, p > 0.05). Mean ICC between the Polar V800 versus high-speed camera was 0.91 for the SJ and CMJ tests, however, a significant systematic bias ± random error (0.97 ± 2.60 cm; p = 0.01) was detected in CMJ test. The Polar V800 offers valid, compared to force platform, and reliable information about vertical jump height performance in physically active healthy young men.Key points

• The Polar V800 sports watch was shown to be a reliable and valid tool for measuring jumping ability.
• The Polar V800 is a simple, multifunctional, inexpensive and practical device that offers adequate information about the vertical jump height performance in physically active healthy young men.
• It would also be interesting to demonstrate the reliability and validity of the Polar V800 sports watch to assess vertical jump height in highly trained athletes or other populations.

Key words: Jumping ability, squat jump, countermovement jump, pulsometer, Bland Altman plot, intraclass correlation coefficient     

Muscle Strength and Qualitative Jump-Landing Differences in Male and Female Military Cadets: The Jump-ACL Study

Recent studies have focused on gender differences in movement patterns as risk factors for ACL injury. Understanding intrinsic and extrinsic factors which contribute to movement patterns is critical to ACL injury prevention efforts. Isometric lower- extremity muscular strength, anthropometrics, and jump-landing technique were analyzed for 2,753 cadets (1,046 female, 1,707 male) from the U.S. Air Force, Military and Naval Academies. Jump- landings were evaluated using the Landing Error Scoring System (LESS), a valid qualitative movement screening tool. We hypothesized that distinct anthropometric factors (Q-angle, navicular drop, bodyweight) and muscle strength would predict poor jump-landing technique in males versus females, and that female cadets would have higher scores (more errors) on a qualitative movement screen (LESS) than males. Mean LESS scores were significantly higher in female (5.34 ± 1.51) versus male (4.65 ± 1.69) cadets (p < 0.001). Qualitative movement scores were analyzed using factor analyses, yielding five factors, or “patterns”, contributing to poor landing technique. Females were significantly more likely to have poor technique due to landing with less hip and knee flexion at initial contact (p < 0.001), more knee valgus with wider landing stance (p < 0. 001), and less flexion displacement over the entire landing (p < 0.001). Males were more likely to have poor technique due to landing toe-out (p < 0.001), with heels first, and with an asymmetric foot landing (p < 0.001). Many of the identified factor patterns have been previously proposed to contribute to ACL injury risk. However, univariate and multivariate analyses of muscular strength and anthropometric factors did not strongly predict LESS scores for either gender, suggesting that changing an athlete’s alignment, BMI, or muscle strength may not directly improve his or her movement patterns.

Key points

• Important differences in male and female landing technique can be captured using a qualitative movement screen: the Landing Error Scoring System (LESS).
• Female cadets were more likely to land with shallow sagittal flexion, wide stance width, and more pronounced knee flexion.
• Male cadets were more likely to exhibit a heel-strike or asymmetric foot-strike and to land with toe out.
• Lower extremity muscle strength, Q-angle, and navicular drop do not significantly predict landing movement pattern in male or female cadets.

Key words: Jump-landing, ACL injury risk, motor patterns, qualitative movement screen     

The Lower Extremity Biomechanics of Single- and Double-Leg Stop-Jump Tasks

The anterior cruciate ligament (ACL) injury is a common occurrence in sports requiring stop-jump tasks. Single- and double-leg stop-jump techniques are frequently executed in sports. The higher risk of ACL injury in single-leg drop landing task compared to a double-leg drop landing task has been identified. However the injury bias between single- and double-leg landing techniques has not been investigated for stop-jump tasks. The purpose of this study was to determine the differences between single- and double-leg stop-jump tasks in knee kinetics that were influenced by the lower extremity kinematics during the landing phase. Ground reaction force, lower extremity kinematics, and knee kinetics data during the landing phase were obtained from 10 subjects performing single- and double-leg stop-jump tasks, using motion-capture system and force palates. Greater peak posterior and vertical ground reaction forces, and peak proximal tibia anterior and lateral shear forces (p < 0.05) during landing phase were observed of single-leg stop-jump. Single-leg stop-jump exhibited smaller hip and knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground (p < 0.05). We found smaller peak hip and knee flexion angles (p < 0.05) during the landing phase of single-leg stop-jump. These results indicate that single-leg landing may have higher ACL injury risk than double-leg landing in stop-jump tasks that may be influenced by the lower extremity kinematics during the landing phase.

Key points

• Non-contact ACL injuries are more likely to occur during the single-leg stop-jump task than during the double-leg stop-jump task.
• Single-leg stop-jump exhibited greater peak proximal tibia anterior and lateral shear forces, and peak posterior and vertical ground reaction forces during the landing phase than the double-leg stop-jump task.
• Single-leg stop-jump exhibited smaller hip flexion angle, knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground.
• Single-leg stop-jump exhibited greater peak knee extension and valgus moment during the landing phase than the double-leg stop-jump task.
• Single-leg stop-jump extended the hip joint at initial foot contact with the ground.

Key words: Anterior cruciate ligament, kinematics, kinetics, ground reaction force     

Muscle Architectural and Force-Velocity Curve Adaptations following 10 Weeks of Training with Weightlifting Catching and Pulling Derivatives

The aims of this study were to examine the muscle architectural, rapid force production, and force-velocity curve adaptations following 10 weeks of resistance training with either submaximal weightlifting catching (CATCH) or pulling (PULL) derivatives or pulling derivatives with phase-specific loading (OL). 27 resistance-trained men were randomly assigned to the CATCH, PULL, or OL groups and completed pre- and post-intervention ultrasound, countermovement jump (CMJ), and isometric mid-thigh pull (IMTP). Vastus lateralis and biceps femoris muscle thickness, pennation angle, and fascicle length, CMJ force at peak power, velocity at peak power, and peak power, and IMTP peak force and force at 100-, 150-, 200-, and 250 ms were assessed. There were no significant or meaningful differences in muscle architecture measures for any group (p > 0.05). The PULL group displayed small-moderate (g = 0.25-0.81) improvements in all CMJ variables while the CATCH group displayed trivial effects (g = 0.00-0.21). In addition, the OL group displayed trivial and small effects for CMJ force (g = -0.12-0.04) and velocity variables (g = 0.32-0.46), respectively. The OL group displayed moderate (g = 0.48-0.73) improvements in all IMTP variables while to PULL group displayed small-moderate (g = 0.47-0.55) improvements. The CATCH group displayed trivial-small (g = -0.39-0.15) decreases in IMTP performance. The PULL and OL groups displayed visible shifts in their force-velocity curves; however, these changes were not significant (p > 0.05). Performing weightlifting pulling derivatives with either submaximal or phase-specific loading may enhance rapid and peak force production characteristics. Strength and conditioning practitioners should load pulling derivatives based on the goals of each specific phase, but also allow their athletes ample exposure to achieve each goal. Key points

• There were no significant or practically meaningful changes in vastus lateralis or biceps femoris muscle thickness, pennation angle, or fascicle length for any group.
• The PULL group produced the greatest CMJ force at peak power, velocity at peak power, and peak power adaptations.
• The PULL and OL groups produced similar benefits in rapid force production; however, peak force adaptations favored the OL group.
• Despite visible shifts in the force-velocity curves of the PULL and OL groups, none of the changes were statistically significant.

Key words: Weightlifting, Olympic weightlifting, countermovement jump, isometric-mid thigh pull, force-velocity profile, rate of force development     

Comparison of A Single Vibration Foam Rolling and Static Stretching Exercise on the Muscle Function and Mechanical Properties of the Hamstring Muscles

Knee extension and hip flexion range of motion (ROM) and functional performance of the hamstrings are of great importance in many sports. The aim of this study was to investigate if static stretching (SS) or vibration foam rolling (VFR) induce greater changes in ROM, functional performance, and stiffness of the hamstring muscles. Twenty-five male volunteers were tested on two appointments and were randomly assigned either to a 2 min bout of SS or VFR. ROM, counter movement jump (CMJ) height, maximum voluntary isometric contraction (MVIC) peak torque, passive resistive torque (PRT), and shear modulus of semitendinosus (ST), semimembranosus (SM), and biceps femoris (BF_lh), were assessed before and after the intervention. In both groups ROM increased (SS = 7.7%, P < 0.01; VFR = 8.8%, P < 0.01). The MVIC values decreased after SS (-5.1%, P < 0.01) only. Shear modulus of the ST changed for -6.7% in both groups (VFR: P < 0.01; SS: P < 0.01). Shear modulus decreased in SM after VFR (-6.5%; P = 0.03) and no changes were observed in the BF_lh in any group (VFR = -1%; SS = -2.9%). PRT and CMJ values did not change following any interventions. Our findings suggest that VFR might be a favorable warm-up routine if the goal is to acutely increase ROM without compromising functional performance. Key points

• Both interventions (vibration foam rolling and static stretching) lead to the similar increase in hip flexion range of motion.
• Vibration foam rolling of the hamstrings reduces muscle stiffness of the Semitendinosus (ST) and Semimembranosus (SM) muscles, while static stretching lead to a reduction in muscle shear modulus of the ST only.
• Maximal voluntary isometric contraction peak torque is reduced after prolonged (2 min) static stretching but not after a similar duration of vibration foam rolling.

Key words: Shear modulus, range of motion, muscle stiffness, self-myofascial release, muscle performance, force production     

A Comparison of the Habitual Landing Strategies from Differing Drop Heights of Parkour Practitioners (Traceurs) and Recreationally Trained Individuals

Parkour is an activity that encompasses methods of jumping, climbing and vaulting. With landing being a pertinent part of this practise, Parkour participants (traceurs) have devised their own habitual landing strategies, which are suggested to be a safer and more effective style of landing. The purpose of this study was to compare the habitual landing strategies of traceurs and recreationally trained individuals from differing drop heights. Comparisons between landing sound and mechanical parameters were also assessed to gauge the level of landing safety. Ten recreationally trained participants and ten traceurs performed three landings from 25% and 50% body height using their own habitual landing strategies. Results at 25% showed significantly lower maximal vertical force (39.9%, p < 0.0013, ES = -1.88), longer times to maximal vertical force (68.6%, p < 0.0015, ES = 1.72) and lower loading rates (65.1%, p < 0.0002, ES = -2.22) in the traceur group. Maximal sound was also shown to be lower (3.6%), with an effect size of -0.63, however this was not statistically significant (p < 0.1612). At 50%, traceurs exhibited significantly different values within all variables including maximal sound (8.6%, p < 0.03, ES = -1.04), maximal vertical force (49.0%, p < 0.0002, ES = -2.38), time to maximal vertical force (65.9%, p < 0.0067, ES = 1.32) and loading rates (66.3%, p < 0.0002, ES = -2.00). Foot strike analysis revealed traceurs landed using forefoot or forefoot-midfoot strategies in 93.2% of trials; whereas recreationally trained participants used these styles in only 8.3% of these landings. To conclude, the habitual landings of traceurs are more effective at lowering the kinetic landing variables associated with a higher injury risk in comparison to recreationally trained individuals. Sound as a measure of landing effectiveness and safety holds potential significance; however requires further research to confirm.

Key points

• Habitual traceur landings were observed to be safer landing techniques in comparison to those utilised by recreationally trained individuals, due to the lower maximal vertical forces, slower times to maximal vertical force, lesser loading rates and lower maximal sound.
• Traceurs predominantly landed with the forefoot only, whereas recreationally trained individuals habitually utilised a forefoot to heel landing strategy.
• The habitual landing techniques performed by traceurs may be beneficial for other landing sports to incorporate into training to reduce injury.

Key words: Kinetics, forefoot, Parkour, dissipation, kinematics     

Jumping and Landing Techniques in Elite Women’s Volleyball

Volleyball has become one of the most widely played participant sports in the world. Participation requires expertise in many physical skills and performance is often dependent on an individual’s ability to jump and land. The incidence of injury in volleyball is similar to the rates reported for sports that are considered more physical contact sports. Though the most common source of injury in volleyball is the jump landing sequence, little research exists regarding the prevalence of jumping and landing techniques. The purpose of this study was to quantify the number of jumps performed by female volleyball players in competitive matches and to determine the relative frequency of different jump-landing techniques. Videotape recordings of two matches among four volleyball teams were analyzed for this study. Each activity was categorized by jump type (offensive spike or defensive block) and phase (jump or landing). Phase was subcategorized by foot use patterns (right, left, or both). Each of the players averaged nearly 22 jump-landings per game. Foot use patterns occurred in unequal amounts (p < 0.001) with over 50% of defensive landings occurring on one foot. Coaches, physical educators, and recreation providers may utilize the findings of this inquiry to help prevent injuries in volleyball.

Key Points

• The incidence of injury in volleyball is nearly equivalent to injury rates reported for ice hockey and soccer.
• Most injuries in volleyball occur during the jump landing sequence, but few data exist regarding jump landing techniques for elite female players.
• Our data indicate that the vast majority of jumps utilize two feet, but approximately half of landings occur with only one foot.
• Coaches, physical educators, and recreation providers may utilize the findings of this inquiry to prevent possible injuries in athletes, students, or those who participate in volleyball for recreational purposes.

Key words: Knee injury, jumping technique, female, leap, frequency     

Relationships Between Lower-Body Muscle Structure and,Lower-Body Strength,Explosiveness and Eccentric Leg Stiffness in Adolescent Athletes

The purpose of the present study was to determine whether any relationships were present between lower-body muscle structure and, lower-body strength, variables measured during a countermovement jump (CMJ) and squat jump (SJ), and eccentric leg stiffness, in adolescent athletes. Thirty junior male (n = 23) and female (n = 7) surfing athletes (14.8 ± 1.7 y; 1.63 ± 0.09 m; 54.8 ± 12.1 kg) undertook lower-body muscle structure assessment with ultrasonography and performed a; CMJ, SJ and an isometric mid-thigh pull (IMTP). In addition, eccentric leg stiffness was calculated from variables of the CMJ and IMTP. Moderate to very large relationships (r = 0.46-0.73) were identified between the thickness of the vastus lateralis (VL) and lateral gastrocnemius (LG) muscles, and VL pennation angle and; peak force (PF) in the CMJ, SJ and IMTP. Additionally, moderate to large relationships (r = 0.37-0.59) were found between eccentric leg stiffness and; VL and LG thickness, VL pennation angle, and LG fascicle length, with a large relationship (r = 0.59) also present with IMTP PF. These results suggest that greater thickness of the VL and LG were related to improved maximal dynamic and isometric strength, likely due to increased hypertrophy of the extensor muscles. Furthermore, this increased thickness was related to greater eccentric leg stiffness, as the associated enhanced lower-body strength likely allowed for greater neuromuscular activation, and hence less compliance, during a stretch-shortening cycle.

Key points

• Greater thickness of the VL and LG muscles were significantly related to an enhanced ability to express higher levels of isometric and dynamic strength, and explosiveness in adolescent athletes.
• Isometric strength underpinned performance in the CMJ and SJ in these athletes.
• Greater lower-body isometric strength was significantly related to eccentric leg stiffness, which is potentially the result of greater neuromuscular activation in the muscle-tendon unit.

Key words: Muscle architecture, children, associations, ultrasound