The use of various strength-power tests as predictors of sprint running performance

AIM: The aim of the present study was to assess the relationship between various strength-power tests and maximal running velocity parameters. METHODS: Nine trained males were tested on four separate occasions. On the first occasion the maximum running velocity (MRV), stride rate (SR) and stride length (SL) were measured over 35 m. On the second occasion maximal vertical jumps (squat jump [SJ], standing broad jump [SBJ], counter movement jump [CMJ] and drop jumps [DJ] from heights of 30, 50 and 80 cm) were performed on a force platform. On the third occasion the maximal bilateral isometric force (MBIF) of leg extensors and the force time characteristics (f-t 10-30%, f-t 10-60% and f-t 10-90%) were determined using a leg extension machine connected to a force plate. On the final fourth occasion peak anaerobic power was measured via repeated 6 sec maximum cycle sprints. Pearson product-moment correlation coefficients were calculated for all the aformentioned parameters. RESULTS: The correlation coefficients showed that MRV correlated significantly with f-t 10-60% and DJ 30 (r=-0.73 and r=0.73, P<0.05 respectively). In addition, SR and SL showed significant relationships with f-t 10-60% (r=-0.82, P<0.01 and r=0.75, P<0.05 respectively). CONCLUSION: The present findings suggest that the ability to produce force quickly, as measured by the time to achieve 60% of maximum voluntary contraction is related to sprinting performance, with the coefficient of determination accounting for 53% of the variance in the data. These data also show that sprinting ability is linked with DJ performance, especially the drop jump from a height of 30 cm. It is suggested that the above tests may prove useful in preparing and testing the sprinting ability and sprint specific strength levels.     

Leg power and hopping stiffness: relationship with sprint running performance

PURPOSE: Although sprint performance undoubtedly involves muscle power, the stiffness of the leg also determines sprint performance while running at maximal velocity. Results that include both of these characteristics have not been directly obtained in previous studies on human runners. We have therefore studied the link between leg power, leg stiffness, and sprint performance. METHODS: The acceleration and maximal running velocity developed by 11 subjects (age 16 +/- 1) during a 40-m sprint were measured by radar. Their leg muscle volumes were estimated anthropometrically. Leg power was measured by an ergometric treadmill test and by a hopping test. Each subject executed a maximal sprint acceleration on the treadmill equipped with force and speed transducers, from which forward power was calculated. A hopping jump test was executed at 2 Hz on a force platform. Leg stiffness was calculated using the flight and contact times of the hopping test. RESULTS: The treadmill forward leg power was correlated with both the initial acceleration (r = 0.80, P < 0.01) and the maximal running velocity (r = 0.73, P < 0.05) during track sprinting. The leg stiffness calculated from hopping was significantly correlated with the maximal velocity but not with acceleration. CONCLUSION: Although muscle power is needed for acceleration and maintaining a maximal velocity in sprint performance, high leg stiffness may be needed for high running speed. The ability to produce a stiff rebound during the maximal running velocity could be explored by measuring the stiffness of a rebound during a vertical jump.     

Is muscle power related to running speed with changes of direction?

BACKGROUND: The purpose of this study was to identify the relationships between leg muscle power and sprinting speed with changes of direction. METHODS: EXPERIMENTAL DESIGN: the study was designed to describe relationships between physical qualities and a component of sports performance. SETTING: testing was conducted in an indoor sports hall and a biomechanics laboratory. PARTICIPANTS: 15 male participants were required to be free of injury and have recent experience competing in sports involving sprints with changes of direction. MEASURES: subjects were timed in 8 m sprints in a straight line and with various changes of direction. They were also tested for bilateral and unilateral leg extensor muscle concentric power output by an isokinetic squat and reactive strength by a drop jump. RESULTS: The correlations between concentric power and straight sprinting speed were non-significant whereas the relationships between reactive strength and straight speed were statistically significant. Correlations between muscle power and speed while changing direction were generally low and non-significant for concentric leg power with some moderate and significant (p<0.05) coefficients found for reactive strength. The participants who turned faster to one side tended to have a reactive strength dominance in the leg responsible for the push-off action. CONCLUSIONS: The relationships between leg muscle power and change-of-direction speed were not consistent. Reactive strength as measured by the drop jump appears to have some importance for lateral change-of-direction speed, possibly because of similar push-off actions. It was concluded that reactive strength of the leg extensor muscles has some importance in change-of-direction performance but the other technical and perceptual factors than influence agility performance should also be considered.     

Influence of ethnic origin on predictive parameters of performance in sprint running in prepubertal boys

Afro-American and Caribbean athletes have long dominated sprint running, although the reasons for their disproportionate success remain unclear. The studies of sprinting ability in blacks versus whites have shown contradictory results. This study compared the anthropometric measurements and the physical test results (vertical jump and sprint) of Caucasian and Afro-Caribbean prepubertal boys. Seventeen healthy untrained prepubertal boys, 8 Caucasians and 9 Afro-Caribbeans (11.49 +/- 0.74 years) performed vertical jump tests (a countermovement jump according to the Sargent method, using Abalakov material) and short sprints (30 m). Age, height, weight, and fat mass percentage were also recorded. The sprints were filmed to determine the number of strides over the 30 m. No significant difference was noted for sprint performance between the Caucasians and Afro-Caribbeans (respectively, 5.59 seconds +/- 0.44 vs. 5.51 s +/- 0.50). The predictors of sprint performance differed between the two groups: the vertical jump test was the main predictor for the Caucasian group, whereas the stride number/height ratio was the main predictor for the Afro-Caribbean group. This last group had better ratio (0.14 +/- 0.15 vs. 0.16 +/- 0.02, p < 0.05) and better jump test results (36.77 cm +/- 2.90 vs. 31.12 cm +/- 4.76, p < 005). The prepubertal Afro-Caribbeans seemed to be endowed to run faster but they did not. We hypothesize that they were unable to use their greater leg strength to develop an optimal stride. Further study is needed to investigate what occurs at other maturational stages.     

Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players

Background: A high level of strength is inherent in elite soccer play, but the relation between maximal strength and sprint and jumping performance has not been studied thoroughly.

Objective: To determine whether maximal strength correlates with sprint and vertical jump height in elite male soccer players.

Methods: Seventeen international male soccer players (mean (SD) age 25.8 (2.9) years, height 177.3 (4.1) cm, weight 76.5 (7.6) kg, and maximal oxygen uptake 65.7 (4.3) ml/kg/min) were tested for maximal strength in half squats and sprinting ability (0–30 m and 10 m shuttle run sprint) and vertical jumping height.

Result: There was a strong correlation between maximal strength in half squats and sprint performance and jumping height.

Conclusions: Maximal strength in half squats determines sprint performance and jumping height in high level soccer players. High squat strength did not imply reduced maximal oxygen consumption. Elite soccer players should focus on maximal strength training, with emphasis on maximal mobilisation of concentric movements, which may improve their sprinting and jumping performance.

     

Training-specific muscle architecture adaptation after 5-wk training in athletes

PURPOSE: This study examined changes in the muscle size, muscle architecture, strength, and sprint/jump performances of concurrently training athletes during 5 wk of "altered" resistance training (RT). METHODS: Eight female and 15 male athletes performed 4 wk of sprint, jump, and resistance training in addition to their sports training (standardization) before adopting one of three different programs for 5 wk: 1) squat lift training (SQ, N = 8) with sprint/jump training; 2) forward hack squat training (FHS, N = 7) with sprint/jump training; or 3) sprint/jump training only (SJ, N = 8). Muscle size, fascicle angle, and fascicle length of the vastus lateralis (VL) and rectus femoris (RF) muscles (using ultrasound procedures) as well as 20-m sprint run, vertical jump, and strength performance changes were examined. RESULTS: A small increase in VL fascicle angle in SQ and FHS was statistically different to the decrease in SJ subjects (P < 0.05 at distal, P < 0.1 at proximal). VL fascicle length increased for SJ only (P < 0.05 at distal, P < 0.1 at proximal) and increased in RF in SQ subjects (P < 0.05). Muscle thickness of VL and RF increased in all training groups (P < 0.05) but only at proximal sites. There were no between-group differences in squat, forward hack squat, or isokinetic strength performances, or in sprint or jump performances, despite improvements in some of the tests across the groups. CONCLUSIONS: Significant muscle size and architectural adaptations can occur in concurrently training athletes in response to a 5-wk training program. These adaptations were possibly associated with the force and velocity characteristics of the training exercises but not the movement patterns. Factors other than, or in addition to, muscle architecture must mediate changes in strength, sprint, and jump performance.     

Kinematic,strength, and stiffness adaptations after a short‐term sled towing training in athletes

One of the most frequently used methods for training the sprint‐specific strength is the sled towing. To date, no studies have been conducted to explore the effects of this method after a training period in well‐trained athletes. The purpose of this study was to determine the effects of 4 weeks of resisted sprint training with sled towing. Twenty‐two trained athletes experienced in the use of weighted sled (WS) participated in the study. They conducted the same 3‐week training to level their initial condition. After that they were distributed in two groups, unresisted (UR) and WS training. They carried out the same 4‐week, 2 days/week sprint‐specific training, only differing in that the experimental group performed sprints with a (WS) which caused a reduction of 7.5% of their maximum velocity. Pre‐ and posttest were conducted which included the measurement of sprint kinematics, muscular strength (including isoinertial, isokinetic, and jump measurements), and sprinting stiffness (leg and vertical). Results show different adaptations in the groups although no interaction effect was found. The WS group improved the velocity in the transition phase, while the UR group improved the velocity in the maximum velocity phase. No improvements in the height of the jump tests were found.     

Isokinetic strength and anaerobic power of elite, subelite and amateur French soccer players

Information about the influence of different practice levels on physical characteristics of a large number of soccer players is lacking. Therefore we assessed muscular strength and anaerobic power of elite, subelite and amateur soccer players to clarify what parameters distinguish the top players from the less successful. We tested 95 soccer players from the French first division (elite), second division (subelite), and amateurs and determined the isokinetic strength of the knee extensor and flexor muscles at angular velocities from -120 degrees x s(-1) to 300 degrees x s(-1). Vertical jump, 10 m sprint, 30 m sprint and maximum ball speed during shooting were also measured. The elite players had higher knee flexor torque than the amateurs at all angular velocities (p < 0.05), except at 300 degrees x s(-1). The hamstring/quadriceps ratios proposed with two different methods were significantly lower in the amateur group than in the elite group (p < 0.05), except at 300 degrees x s(-1). Maximum ball speed during shooting and speed over 30 m sprint were not different between elite, subelite, and amateur players while speed over a 10 m sprint was significantly slower in amateur players and faster in the elite group (p < 0.05). Although performance in soccer is not determined only by measurable variables, professional players differ from amateurs in terms of knee flexor muscle strength and short-distance sprinting speed. Based on these findings we conclude that hamstring strength is extremely important in soccer players for joint stabilization during various tasks, notably in eccentric action. Further, short-sprinting performance may mirror actual game situations at high level and could be an important determinant of match-winning actions.     

Physical performance characteristics of high-level female soccer players 12-21 years of age

Performance assessment has become an invaluable component of monitoring player development and within talent identification programs in soccer, yet limited performance data are available for female soccer players across a wide age range. The aim of this study was to describe the physical performance characteristics of female soccer players ranging in age from 12 to 21 years. High-level female soccer players (n=414) were evaluated on linear sprinting (36.6 m with 9.1 m splits), countermovement jump (CMJ), and two agility tests. Separate one-way ANOVAs were used to compare performance characteristics between (1) each year of chronological age and (2) three age groups: 12-13 years, n=78, 14-17 years, n=223, and 18-21 years, n=113. Mean linear sprint speed over 9.1 m was similar across all chronological ages, however sprint speed over the final 9.1 m, CMJ height and agility scores improved until approximately 15-16 years. Outcomes from the group data indicated better performance on all tests for the 14-17-year-old group compared with the 12-13-year-old group. Additionally, sprint speed on the second and fourth 9.1 m splits and 36.6 m sprint speed as well as performance on the Illinois agility test was better in the 18-21-year-old group compared with the 14-17-year-old group. The findings from this study indicate that marked improvements of high intensity short duration work occur up until 15-16 years. Smaller gains in performance were observed beyond 16 years of age as evidenced by better performance on 36.6 m sprint speed, several sprint splits and the Illinois agility test in the college aged players (i.e., 18-21-year-old group).     

Motor performance status in 10 to 17-year-old Estonian girls

The improvement of motor abilities is associated with the periodical acceleration of changes in adolescents of both sexes. The present cross-sectional study is aimed at establishing smooth curves of motor performance status in 10 to 17-year-old girls. Motor performance was tested in 902 girls with the aid of 30 m dash, standing long jump, vertical jump, pushing a stuffed ball (2 kg), standing quintuplet jump, isometric strength of back extensor muscles, trunk forward flexion and 1-min ergocycling at the highest possible rate. Statistically significant differences of all studied motor abilities between the age groups of 10-12 were indicated. In height and body mass the most pronounced differences (on average 6.5 cm and 7.7 kg, respectively) appeared between the age groups of 12 and 13. At the age of 13 the group results were statistically higher than those at 12 in pushing a stuffed ball, vertical jump, quintuplet jump, strength of back extensors muscle, 30 m dash and ergocycling test, but not in standing long jump and trunk forward flexion. At the age of 14 the performance was not higher than at 13, except in the vertical jump and quintuplet jump. From 14 to 16 years of age differences reappeared in the results of vertical jump, quintuplet jump, pushing a stuffed ball, 1-min cycling and trunk forward flexion but not in the 30 m dash and standing long jump. The lack of significant differences between the age groups of 16 and 17 indicated the final stabilization of tested motor abilities. The obtained results suggest the existence of several periods in motor performance status in 10 to 17-year-old Estonian girls: 1) The biggest differences in the mean results of the tests on motor abilities occurred between ages 10-11, 11-12 and 12-13, which coincide with the biggest differences in height and weight at the same age. 2) The differences in the mean results of most tests on motor abilities stabilized between the age groups of 13 and 14. The mean results of 14-year-old girls were lower in some tests compared to the results of 13-year-olds. 3) The positive differences in the mean results remained between the age groups of 14-15 and 15-16 (excluding the sprint velocity and standing long jump). 4) The final stabilization of motor abilities occurred at the age of 16 to 17.     

Knee extensor stiffness and functional performance

ObjectiveTo determine the reliability of a new method to measure the stiffness of the knee extensors and thereafter establish the relationship between knee extensor stiffness and, jump and running performance.SettingA professional rugby union football club and a university laboratory.ParticipantsThirty semi-elite male rugby union players.Main outcome measuresThe stiffness of the knee extensors across loads ranging from 30 to 70% maximal voluntary isometric contraction, 20 m sprint, maximal squat strength, countermovement-jump and drop-jump performance was assessed.ResultsWithin trial variation (coefficient of variation—range 5.41–7.45%) for all five loads (30, 40, 50, 60 and 70%) and test–retest reliability (intra-class correlation coefficients—range 0.92–0.96) were deemed acceptable. Knee extensor stiffness was found to have no significant relationship (P>0.05) to any of the functional performance measures (r=−0.160–0.172).ConclusionIt was concluded that the new protocol to assess the stiffness of the knee extensors was reliable, however the relationship between knee extensor stiffness and measures of strength, power and speed was weak and non-significant.     

Poor relationship between strength and power qualities and agility performance

AIM: Despite the important role of agility in successful performance in many team and racket sports, little is known about their physiological and muscular basis. The aim of this study was to examine the relationship between the leg extensor strength and power and agility performance. METHODS: Male physical education students (n=76) were assessed by means of 3 typical agility performance tests (lateral stepping, 20-yard shuttle run, and slalom run). Six tests of leg extensor strength (isoinertial squat, isometric squat, and one-leg rising) and power (squat jump power, hopping power, and standing long jump distance) were also obtained. RESULTS: The correlations between strength and power, and each agility performance were generally low. As a consequence, the multiple correlation coefficients between strength and power predictors and agility, albeit significant (P<0.01), were also rather low (r=0.33, 0.44, and 0.35 for the lateral stepping, 20-yard shuttle run, and slalom run, respectively). The highest relationship with each of the agility tests was revealed by the one-leg rising test (r within -0.3 and -0.44; P<0.02). CONCLUSION: The results of the present study suggest that most of the multijoint leg extensor strength and power measures are poor predictors of agility in physically active men. Thus, the effects of interventions aimed towards the improvement of functional movement performance may not require evaluation by means of the common tests of muscular strength and power. A more specific approach including both the functional strength tests and functional movement performance tests could be recommended instead.     

Biomechanics of sprint running. A review.

Understanding of biomechanical factors in sprint running is useful because of their critical value to performance. Some variables measured in distance running are also important in sprint running. Significant factors include: reaction time, technique, electromyographic (EMG) activity, force production, neural factors and muscle structure. Although various methodologies have been used, results are clear and conclusions can be made. The reaction time of good athletes is short, but it does not correlate with performance levels. Sprint technique has been well analysed during acceleration, constant velocity and deceleration of the velocity curve. At the beginning of the sprint run, it is important to produce great force/power and generate high velocity in the block and acceleration phases. During the constant-speed phase, the events immediately before and during the braking phase are important in increasing explosive force/power and efficiency of movement in the propulsion phase. There are no research results available regarding force production in the sprint-deceleration phase. The EMG activity pattern of the main sprint muscles is described in the literature, but there is a need for research with highly skilled sprinters to better understand the simultaneous operation of many muscles. Skeletal muscle fibre characteristics are related to the selection of talent and the training-induced effects in sprint running. Efficient sprint running requires an optimal combination between the examined biomechanical variables and external factors such as footwear, ground and air resistance. Further research work is needed especially in the area of nervous system, muscles and force and power production during sprint running. Combining these with the measurements of sprinting economy and efficiency more knowledge can be achieved in the near future.     

Strength and performance asymmetry during maximal velocity sprint running

The aim of this study was to empirically examine the interaction of athlete‐specific kinematic kinetic and strength asymmetry in sprint running. Bilateral ground reaction force and kinematic data were collected during maximal velocity (mean = 9.05 m/s) sprinting for eight athletes. Bilateral ground reaction force data were also collected while the same athletes performed maximal effort squat jumps. Using novel composite asymmetry scores, interactions between kinematic and kinetic asymmetry were compared for the group of sprinters. Asymmetry was greater for kinematic variables than step characteristics, with largest respective values of 6.68% and 1.68%. Kinetic variables contained the largest asymmetry values, peaking at >90%. Asymmetry was present in all kinematic and kinetic variables analyzed during sprint trials. However, individual athlete asymmetry profiles were reported for sprint and jump trials. Athletes' sprint performance was not related to their overall asymmetry. Positive relationships were found between asymmetry in ankle work during sprint running and peak vertical force (r = 0.895) and power (r = 0.761) during jump trials, suggesting that the ankle joint may be key in regulating asymmetry in sprinting and highlighting the individual nature of asymmetry. The individual athlete asymmetry profiles and lack of relationship between asymmetry of limb strength and sprint performance suggest that athletes are not “limb dominant” and that strength imbalances are joint and task specific. Compensatory kinetic mechanisms may serve to reduce the effects of strength or biological asymmetry on the performance outcome of step velocity.     

Fitness testing and career progression in AFL football

Relationships between fitness testing and career progression in the Australian Football League (AFL) are under-explored. This study investigated relationships between anthropometric and fitness tests conducted at the annual AFL National Draft Camp and subsequent career progression of players. A total of 283 players was tested over three consecutive camps (1999-2001). The anthropometric and fitness measures were: height, mass, sum of skinfolds, 20-m sprint test, vertical jump (standing and bilateral running), agility run and a multi-stage incremental shuttle run. The five outcome variables were: drafted (yes/no), AFL debut (yes/no), number of AFL games played to the end of 2003, and subjective ratings of career potential and career value (5-point scale). Of 205 players (72%) subsequently drafted, 166 (59%) eventually made their AFL debut. Players drafted to AFL clubs were faster over 5 m, 10 m and 20 m, ran further in the shuttle run and ran marginally faster in the agility test than players not drafted. Multi-regression analysis showed small to moderate correlations (r = 0.27-0.31) between the designated outcome variables and selected fitness tests: 20-m sprint time (faster), agility run test (faster), and running vertical jump (higher absolute height and smaller difference between left and ride sides). Regression analysis for the standing vertical jump relative to standing reach height showed a counterintuitive negative correlation with positive outcomes, possibly reflecting non-compliance with testing procedures by the less successful athletes. We conclude that the 20-m sprint, jump, agility and shuttle run tests have a small but important association with career progression of AFL footballers.     

Strength and speed characteristics of elite, subelite, and recreational young soccer players

The purpose of the present study was to compare maximal isometric force, force-time curve characteristics, pedaling rate, vertical jump, and sprint performance among young soccer players from different competition levels. Fifty-four (54) young soccer players were divided into three groups according to competition level: the elite group (n=18) consisted of soccer players from the national youth soccer team of Greece, the subelite group (n=18) consisted of youth soccer players who participated in the local championship, and the recreational group (n=18) consisted of recreational soccer players. All groups were evaluated for maximal isometric force, explosive force at 100 msec, peak force relative to body mass, rate of force development, squat and drop jump heights, 10 m sprint time, and pedaling rate. The elite group presented significantly (p < 0.05) higher maximal isometric force, vertical jump height, and pedaling rate, and lower 10 m sprint time in comparison with the subelite and recreational groups. No significant differences were observed in strength and speed characteristics between the subelite and recreational young soccer players. The findings of the present study suggest that the elite young soccer players can be distinguished from subelite and recreational young soccer players in strength and speed characteristics. These strength and speed measures can be used for strength and speed diagnosis, and for designing and evaluating training programs.     

The effect of maturation on adaptations to strength training and detraining in 11–15‐year‐olds

To investigate how maturity status modifies the effects of strength training and detraining on performance, we subjected 33 young men to 8 weeks of strength training twice per week followed by 8 weeks without training. Changes in performance tests were analyzed in three maturity groups based on years from/to age of predicted peak height velocity (PHV): pre‐PHV (?1.7 ± 0.4 years; n = 10), mid‐PHV (?0.2 ± 0.4 years; n = 11), and post‐PHV (1.0 ± 0.4 years; n = 12). Mean training effects on one repetition maximum strength (3.6–10.0%), maximum explosive power (11–20%), jump length (6.5–7.4%), and sprint times (?2.1% to ?4.7%) ranged from small to large, with generally greater changes in mid‐ and post‐PHV groups. Changes in force–velocity relationships reflected generally greater increases in strength at faster velocities. In the detraining period, the pre‐PHV group showed greatest loss of strength and power, the post‐PHV group showed some loss of sprint performance, but all groups maintained or improved jump length. Strength training was thus generally less effective before the growth spurt. Maintenance programs are needed for most aspects of explosive performance following strength training before the growth spurt and for sprint speed after the growth spurt.     

A comparison of physiological and anthropometric characteristics among playing positions in junior rugby league players

Objectives: To compare the physiological and anthropometric characteristics of specific playing positions and positional playing groups in junior rugby league players. Methods: Two hundred and forty junior rugby league players underwent measurements of standard anthropometry (body mass, height, sum of four skinfolds), muscular power (vertical jump), speed (10, 20, and 40 m sprint), agility (L run), and estimated maximal aerobic power (multi-stage fitness test) during the competitive phase of the season, after players had obtained a degree of match fitness. Results: Props were significantly (p<0.05) taller, heavier, and had greater skinfold thickness than all other positions. The halfback and centre positions were faster than props over 40 m. Halfbacks had significantly (p<0.05) greater estimated maximal aerobic power than props. When data were analysed according to positional similarities, it was found that the props positional group had lower 20 and 40 m speed, agility, and estimated maximal aerobic power than the hookers and halves and outside backs positional groups. Differences in the physiological and anthropometric characteristics of other individual playing positions and positional playing groups were uncommon. Conclusions: The results of this study demonstrate that few physiological and anthropometric differences exist among individual playing positions in junior rugby league players, although props are taller, heavier, have greater skinfold thickness, lower 20 and 40 m speed, agility, and estimated maximal aerobic power than other positional playing groups. These findings provide normative data and realistic performance standards for junior rugby league players competing in specific individual positions and positional playing groups.     

Velocity specificity of weight training for kayak sprint performance

PURPOSE: Athletes often use weight training to prepare for sprint events, but the effectiveness of different types of weight training for sprinting is unclear. We have therefore investigated the effect of slow and explosive weight training on kayak sprint performance. METHODS: Twenty-seven male and 11 female experienced sprint kayakers were randomized to slow weight training, explosive weight training, or control (usual training) groups. Weight training consisted of two sessions per week for 6 wk; in each session the athletes performed 3-4 sets of two sport-specific exercises with a load of 80% 1-repetition-maximum. The two training programs differed only in the time taken to complete the concentric phase of the exercises: slow, 1.7 s; explosive, <0.85 s. To determine the effects of training on sprint acceleration and speed maintenance, the athletes performed 15-m kayaking sprints pre- and posttraining; an electronic timing system provided sprint times at 3.75-, 7.5-, and 15-m marks. RESULTS: Relative to control, both types of weight training substantially improved strength and sprint performance. The improvements in mean sprint time over 15 m in each group were: slow, 3.4%; explosive, 2.3%; control, -0.2% (90% confidence limits for pairwise differences, approximately +/-1.4%). Over the first 3.75 m, the improvements were: slow, 7.1%; explosive, 3.2%; control, 1.4% ( approximately +/-2.6%). Over the last 7.5 m, the improvements were: slow, 2.1%; explosive, 3.0%; control, -0.8% ( approximately +/-1.9%). CONCLUSIONS: Slow weight training is likely to be more effective than explosive training for improving the acceleration phase of sprinting, when force is high throughout the length of the stroke. Explosive weight training may be more effective in speed maintenance, when forces are developed rapidly over a short period at the start of the stroke.     

Leg ability factors in tennis players

We investigated the effects of leg stiffness on running speed, jump height and leg power in 13 male 2(nd)- and 3(rd)-series ranked tennis players (23 ± 3 years old, 73.2 ± 8.4 kg, 1.81 ± 0.06 m). Leg stiffness and jump height were assessed using jumping and hopping tests. Mean running speeds over 20 m and 40 m (speed?? and speed??, respectively) were determined from a sprint test. Theoretical maximal leg power (P(maxth)) was extrapolated from a force-velocity test performed on a cycle ergometer. Leg stiffness averaged 478.7 ± 181.7 N.m?1.kg?1 (34,808 ± 12,573 N.m?1. It was significantly correlated to speed?? and counter movement jump height (r=0.60, P=0.028 and r=0.58, P=0.0407, respectively). There were also significant correlations between P (maxth) and counter-movement jump height (r=0.59, P=0.0335) and between P(maxth) and speed?? (r=0.58, P=0.0393). This study characterizes leg stiffness in tennis players and brings new information concerning the way it is related to several other muscular biomechanical parameters.