Chronic static stretching improves exercise performance

PURPOSE: This study investigated the influence of static stretching exercises on specific exercise performances. METHODS: Thirty-eight volunteers participated in this study. The stretching group (STR) consisted of 8 males and 11 females whose activity was limited to a 10-wk, 40-min, 3-d.wk(-1) static stretching routine designed to stretch all the major muscle groups in the lower extremity. The control group (CON) consisted of 8 males and 11 females who did not participate in any kind of regular exercise routine during the study. Each subject was measured before and after for flexibility, power (20-m sprint, standing long jump, vertical jump), strength (knee flexion and knee extension one-repetition maximum (1RM)), and strength endurance (number of repetitions at 60% of 1RM for both knee flexion and knee extension). RESULTS: STR had significant average improvements (P < 0.05) for flexibility (18.1%), standing long jump (2.3%), vertical jump (6.7%), 20-m sprint (1.3%), knee flexion 1RM (15.3%), knee extension 1RM (32.4%), knee flexion endurance (30.4%) and knee extension endurance (28.5%). The control group showed no improvement. CONCLUSION: This study suggests that chronic static stretching exercises by themselves can improve specific exercise performances. It is possible that persons who are unable to participate in traditional strength training activities may be able to experience gains through stretching, which would allow them to transition into a more traditional exercise regimen.     

Effect of high velocity resistance training on peak torque, cross sectional area and myofibrillar ATPase activity.

The purpose of this investigation was to determine the effect of high velocity resistance (HVR) training on peak torque (PT), cross sectional area (CSA) and myofibrillar ATPase activity of the knee extensors. HVR training was performed in a circuit on hydraulic exercise equipment, 4 times a week for 5 weeks at an angular velocity of approximately 3.14 rad.s-1. Knee extension PT was determined on a Cybex II isokinetic dynamometer and CSA of the quadriceps femoris muscle was assessed using computer tomography (CT) scanning. Muscle biopsies were obtained from the lateral quadriceps muscle and were analyzed for myofibrillar ATPase activity. Knee extension peak torque was significantly increased at 1.57, 2.09, 3.14, 3.66 and 4.19 rad.s-1. Myofibrillar ATPase activity and CSA was also significantly increased after HVR training. These findings showed that short-term high velocity resistance training enhances the in vivo torque/velocity curve especially at fast angular velocities and these changes are partly attributed to an increase in muscle CSA and activity of myofibrillar ATPase.     

Change in knee kinematics during gait after eccentric isokinetic training for quadriceps in subjects submitted to anterior cruciate ligament reconstruction

Knee kinematics after anterior cruciate ligament (ACL) reconstruction is of interest in studies evaluating the effect of training programs. Many studies have addressed knee flexion/extension but not valgus/varus movements. Considering that joint stability is a major concern in ACL reconstruction surgery, movements occurring in the frontal plane of the knee also deserve attention. Knee extensor torque was analyzed by an isokinetic dynamometer and the angular amplitudes and velocities of flexion/extension and valgus/varus movements were analyzed by goniometry during gait 9 months after ACL reconstruction. The analysis was repeated after 3 months of eccentric isokinetic training of the quadriceps in five patients. The gait pattern was also recorded for 10 healthy controls. The knee extensor torque and flexion/extension range of movement during gait increased significantly after training. However, an unexpectedly increased valgus, most pronounced during the swing phase, which may imply adverse effects on the knee, was also observed in the ACL reconstructed knee. The recorded valgus angles may however be overestimated due to crosstalk. Thus, the extent of the increased valgus, as well as the mechanisms involved and the functional and clinical implications, need clarification before eccentric training after ACL reconstruction can be generally recommended.     

Conditioned patellar tendon reflexes in sprint- and endurance-trained athletes

Tendon reflex characteristics were examined in endurance-trained, sprint-trained, and control subjects (10 SS/group) using a conditioned patellar tendon reflex (PTR) paradigm. Paired PTRs were administered using inter-tap intervals of 0, 25, 50, 75, 150, and 300 ms, with the left leg reflex elicited first, followed by a right leg PTR. A force transducer secured at the ankle was used to measure peak force, time to peak force, and reflex latency. In the unilateral condition, significant differences (P less than 0.05) existed between athletic groups, with the sprint-trained athletes exhibiting greater peak force, faster time to peak force, and faster reflex latency than the endurance athletes. Significant differences (P less than 0.05) also existed for the conditioned reflex. There was a slight depression in reflex parameters in the untrained and sprint-trained groups up to an interval of 50 ms. At later intervals (greater than 50 ms), a marked enhancement occurred in all groups for all dependent measures studied. This longer latency excitatory effect persisted until the 150 ms interval. These differences in both simple and conditioned reflexes in individuals trained for endurance and sprint activities may reflect inherent differences in muscle-tendon stiffness or neural organization.     

短跑支撑期股后肌损伤的动力学分析

目的:本研究通过分析短跑途中跑支撑期下肢关节各种力矩分量,探寻下肢动力学与股后肌损伤的内在联系。方法:8名短跑运动员为受试者,采用即时红外高速摄影技术及三维测力台,引入环节互动动力学方法计算分析短跑最大速度阶段支撑期的下肢关节力矩,研究各种力矩分量(含肌肉力矩、地面反作用力力矩、惯性力矩等)在膝、髋关节处产生的作用,分析在支撑期股后肌的受力及作用情况。结果显示:触地初期,地面反作用力通过膝、髋关节前方,在膝关节处产生伸膝力矩,在髋关节处产生屈髋力矩,为抵抗这一力矩,股后肌群收缩产生屈膝力矩和伸髋力矩分别为231.09±99.04Nm和453.15±199.06Nm。结论:触地初期股后肌承受极大的负荷,是股后肌损伤发生的高危险期。     

Biomechanical analysis of tibial torque and knee flexion angle: implications for understanding knee injury

Knee injuries are common in sports activities. Understanding the mechanisms of injury allows for better treatment of these injuries and for the development of effective prevention programmes. Tibial torque and knee flexion angle have been associated with several mechanisms of injury in the knee. This article focuses on the injury to the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL) and the meniscus of the knee as they relate to knee flexion angle and tibial torque. Hyperflexion and hyperextension with the application of tibial torque have both been implicated in the mechanism of ACL injury. A combination of anterior tibial force and internal tibial torque near full extension puts the ACL at high risk for injury. Hyperflexion also increases ACL force; however, in this position, internal and external tibial torque only minimally increase ACL force. Several successful prevention programmes have been based on these biomechanical factors. Injury to the PCL typically occurs in a flexed or hyperflexed knee position. The effects of application of a tibial torque, both internally and externally, remains controversial. Biomechanical studies have shown an increase in PCL force with knee flexion and the application of internal tibial torque, while others have shown that PCL-deficient knees have greater external tibial rotation. The meniscus must endure greater compressive loads at higher flexion angles of the knee and, as a result, are more prone to injury in these positions. In addition, ACL deficiency puts the meniscus at greater risk for injury. Reducing the forces on the ACL, PCL and meniscus during athletic activity through training, the use of appropriate equipment and safe surfaces will help to reduce injury to these structures.     

Effects of resistance, endurance, and concurrent exercise on training outcomes in men

The specificity of training principle predicts that combining resistance and endurance training (concurrent training) could interfere with the maximum development of strength and endurance capacity that results from either type of training alone. PURPOSE: To determine whether endurance and resistance training performed concurrently produces different performance and physiologic responses compared with each type of training alone. METHODS: Untrained male volunteers were randomly assigned to one of three groups: endurance training (ET, N = 12); resistance training (RT, N = 13); and concurrent training (CT, N = 16). The following measurements were made on all subjects before and after 12 wk of training: weight, percent body fat, peak oxygen consumption (VO(2peak)), isokinetic peak torque and average power produced during single-leg flexion and extension at 60 and 180 degrees.s, one-repetition maximum (1RM) leg press, 1RM bench press, vertical jump height, and calculated jump power. RESULTS: Weight and lean body mass (LBM) increased significantly in the RT and CT groups (P < 0.05). Percent body fat was significantly decreased in the ET and CT groups. VO(2peak) was significantly improved only in the ET group. Peak torque during flexion and extension at 180 degrees.s(-1) increased in the RT group. Improvements in 1RM leg press and bench press were significant in all groups, but were significantly greater in the RT and CT compared to the ET group. Jump power improved significantly only in the RT group, and no group showed a significant change in vertical jump height. CONCLUSIONS: Concurrent training performed by young, healthy men does not interfere with strength development, but may hinder development of maximal aerobic capacity.     

Seasonal variation of selected performance parameters in épée fencers.

In this study, anthropometric measurements were carried out on seven British international male épée fencers, using a maximal treadmill running test, a 20-s Wingate-type test, and isokinetic dynamometry. Testing was conducted on two occasions, 5 to 6 months apart, during mid-off-season (preparation) and mid-in-season (competition) periods. Maximal oxygen intake (VO2max) and maximal respiratory exchange ratio (Rmax) were among the parameters obtained from the treadmill test, while peak and mean anaerobic power outputs were measured during a 20-s maximal effort. Knee extensor and flexor muscle forces from both dominant (leading) and non-dominant (trailing) legs were assessed at 1.04, 3.14 and 4.19 rad sec-1. Statistical analyses revealed lower mean VO2max (P < 0.05) and mean Rmax values (P < 0.02) at the in-season assessments compared with off-season. In-season testing also demonstrated significantly lower peak torques for both dominant and non-dominant knee extensors compared with off-season assessments at all velocities (P < 0.05 to P < 0.004). Furthermore, in-season peak torque for the non-dominant leg flexors was lower (P < 0.03) at 4.19 rad sec-1 than off-season. We conclude that current training practices may account for the observed seasonal variations in performance related physiological parameters in fencers.     

Cross-training effects of a proprioceptive neuromuscular facilitation exercise programme on knee musculature

ObjectivesTo examine the cross-training effects of a proprioceptive neuromuscular facilitation training (PNF) program on peak torque and endurance.DesignFactorial design.ParticipantsTwenty-three males were assigned to a PNF group (n=12) or a control group (n=11).InterventionsThe PNF program included training of the knee extensor and flexor muscles for a period of 8 weeks, exercising three times a week. PNF training included performance of knee movements through range of motion against manual resistance.Main outcome measuresIsokinetic torque and fatigue of the knee flexors and extensors at 60, 180 and 300° s⁻¹ were assessed prior to and immediately after the training period.ResultsAnalysis of variance designs indicated that the PNF group demonstrated significant gains (9.9%) in knee extension torque of the contralateral leg. In contrast, no cross-training effects on peak flexion torque was observed.ConclusionsCross-training effects after PNF exercise were restricted to the knee extensor muscles. Such effects may be important when the aim of a rehabilitation program is to improve the knee extensor muscle function of an immobilized contralateral leg.     

The effects of a supportive knee brace on leg performance in healthy subjects.

Eight healthy volunteers were fitted with a supportive knee brace (Push Brace 'Heavy') to one knee for a duration of four weeks wherein they were tested before, during and after the application to establish the effect of bracing on performance. The tests consisted of isokinetic strength measurement of knee flexion and extension, 60 meter dash, vertical jump height and a progressive horizontal treadmill test until exhaustion (Vmax) with determination of oxygen uptake, heart rate and plasma lactate concentration. Wearing the brace for one day, the performance indicators showed a decline compared with the test before application (base values). Sprint time was 4% longer (p less than 0.01) and Vmax 6% slower (p less than 0.01). Peak torque of knee flexion at 60 and 240 deg.sec-1 was 6% (p less than 0.05) respectively 9% (p less than 0.05) less. Peak extension torque at 60 deg.sec-1 was 9% less (p less than 0.05). While wearing the brace for four weeks, the test performances were practically identical to their base values. After removal of the brace, all test parameters were statistically similar to the base values. Heart rate at submaximal exercise levels was even lower (p less than 0.05). In conclusion, performance in sports with test-like exercise patterns is not affected by the brace tested. Bracing does not "weaken the knee" as it is widely believed in sports practice.     

Strength training effects in prepubescent boys

Possible changes in muscle size and function due to resistance training were examined in prepubertal boys. Thirteen boys (9-11 yr) volunteered for each of the training and control groups. Progressive resistance training was performed three times weekly for 20 wk. Measurements consisted of the following: 1 repetition maximum (RM) bench press and leg press; maximal voluntary isometric and isokinetic elbow flexion and knee extension strength; evoked isometric contractile properties of the right elbow flexors and knee extensors; muscle cross-sectional area (CSA) by computerized tomography at the mid-right upper arm and thigh; and motor unit activation (MUA) by the interpolated twitch procedure. Training significantly increased 1 RM bench press (35%) and leg press (22%), isometric elbow flexion (37%) and knee extension strength (25% and 13% at 90 degrees and 120 degrees, respectively), isokinetic elbow flexion (26%) and knee extension (21%) strength, and evoked twitch torque of the elbow flexors (30%) and knee extensors (30%). There were no significant effects of training on the time-related contractile properties (time to peak torque, half-relaxation time), CSA, or %MUA of the elbow flexors or knee extensors. There was, however, a trend toward increased MUA for the elbow flexors and knee extensors in the trained group. Strength gains were independent of changes in muscle CSA, and the increases in twitch torque suggest possible adaptations in muscle excitation-contraction coupling. Improved motor skill coordination (especially during the early phase of training), a tendency toward increased MUA, and other undetermined neurological adaptations, including better coordination of the involved muscle groups, are likely the major determinants of the strength gains in this study.     

Conditions of isokinetic knee flexion that enhance isokinetic knee extension

The results of two experiments are reported. The purpose of the initial investigation was to determine the effect of isokinetic knee flexion contraction intensity on subsequent knee extension contraction. Seven subjects performed ten isokinetic knee flexion-extension cycles at six isokinetic velocities under two antagonist contraction conditions. In the first condition, isokinetic knee flexion and extension were speed-matched, and, in the second condition, the high-speed condition, knee flexion was 7.85 rad.s-1 irrespective of knee extension velocity, which ranged from 0.52 to 7.85 rad.s-1. Significantly greater isokinetic knee extension measures were observed at low isokinetic velocities and were associated with the high-speed contraction condition. Enhancement of the knee extension contraction was in the initial work phase of the isokinetic contraction. The second experiment was conducted to determine whether the enhancement of the initial work phase could be associated, in part, with passive elastic qualities of the involved musculature. In this study the range of motion for the knee involved musculature. In this study the range of motion for the knee extension-flexion cycles was reduced from the previous 2.01 rad to 1.57 rad. Two isokinetic knee extension velocities were studied (1.57 and 7.85 rad.s-1) under five conditions: initiated from rest, initiated from isometric knee flexion MVC, and with preceding isokinetic knee flexion at 0.52, 4.19, and 7.85 rad.s-1. The hypothesis that knee extension contraction measures would not increase was supported. Based upon the results of the two experiments, it is suggested that the increases in knee extension contraction measures observed in the first experiment are at least partially mediated by the contribution to net torque by passive elastic musculotendinous elements. Further study of this phenomenon with the inclusion of electromyographic measures will allow determination of the presence and contribution of increased neural drive.     

Effect of hamstring flexibility on isometric knee flexion angle-torque relationship

The purpose of this study was to examine the relationship between hamstring flexibility and knee flexion angle–torque relationship. Hamstring flexibility was assessed in 20 subjects (10 men, 10 women) using the straight leg raise (SLR) and active knee extension (AKE) tests. Isometric knee flexion strength was measured at five knee flexion angles while subjects were seated with the test thigh flexed 40° and the trunk flexed 80°. Lower extremities were classified as tight or normal based on the SLR and AKE tests. Peak knee flexion torque, angle of peak torque, and angle–torque relationship were compared between flexibility groups. Peak knee flexion torque was not different between tight and normal groups (SLR P =0.82; AKE P =0.68) but occurred in greater knee flexion (shorter muscle length) in the tight group compared with the normal group (SLR P <0.01; AKE P <0.05). The tight group had higher torque than the normal group at the shortest muscle length tested but lower torque at longer muscle lengths (SLR P <0.001; AKE P <0.001). In conclusion, the angle–torque relationship was shifted to the left in less flexible hamstrings such that knee flexion torque was increased at short muscle lengths and decreased at long muscle lengths when compared with more flexible hamstrings.     

Two-year follow-up on joint stability and muscular function comparing rotating versus fixed bearing TKR

Mobile and fixed bearing in total knee replacement are still discussed controversially. In a retrospective, matched-pair study, we investigated 40 patients with computer-assisted (BrainLAB®) primary total knee replacement (PFC Sigma®, DePuy®) performed two years before. Twenty patients each received a mobile bearing and a fixed bearing. We compared Womac Score, Knee Society Score, postoperative ROM, fluoroscopic measurement of knee stability in flexion and extension and isokinetic muscle strength using a Biodex^TM-3 dynamometer. Both groups showed similar results concerning WOMAC Score (total rotating bearing: 23.05; fixed bearing: 22.57), KSS (rotating bearing: 174.89; fixed bearing: 176.1). Isokinetic muscle force demonstrated statistically significant superior results for knee flexion in the rotating bearing group. Medio-lateral stability revealed statistically significant superior results for the rotating bearing compared to fixed bearing in extension (P>0.05). In flexion only lateral stability was superior (P>0.05). Two-year clinical follow-up after computer-assisted total knee replacement resulted in good clinical outcome with high patient satisfaction. Statistically significant better values for the rotating platform group were found for the medio-lateral stability in extension and the peak flexion torque.     

Physiological adaptations to concurrent endurance training and low velocity resistance training

This study investigated the effects of concurrent endurances and low velocity resistance training (LVR) on measures of strength and aerobic endurance. One group (ES) performed concurrent endurance training 3 days a week and LVR training on alternate days, 3 days a week for 12 weeks. The other group (S) performed only LVR training 3 days a week for 12 weeks without any endurance training. Measurements and increases in training volume were made every three weeks in both groups. Group ES exhibited increases in submaximal exercise responses after 3, 9 and 12 weeks (p less than 0.05). Knee extension peak torque and total work as well as cross-sectional area of quadriceps femoris were significantly increased after 6 and 9 weeks of training in both groups. These findings indicate that no significant differences in strength gains were observed between subjects performing concurrent endurance and resistance training or resistance training only. However, the time-course of adaptations between groups was somewhat different.     

Hamstrings functional properties in athletes with high musculo‐skeletal flexibility

The purpose of this study was to examine whether athletes with highly flexible hamstring muscle‐tendon units display different passive and contractile mechanical properties compared with controls. Flexibility, passive, and active torque–angle properties were assessed in 21 female elite rhythmic gymnasts and 16 female age‐matched athletes. Passive resistance to stretch was measured during knee extension with the hip fixed at 100° of flexion. Concentric isokinetic maximal voluntary knee flexion and extension torques were measured at 60°/s in the same position. Tests of flexibility and passive resistance to stretch indicated a greater flexibility in the gymnasts. Despite no differences between groups in knee flexion and extension peak torque, gymnasts reached knee flexion peak torque at more extended positions (longer muscle lengths) and displayed significantly different torque–angle relations. When active torque was corrected for passive resistance to stretch, differences increased, gymnasts producing more work, and maintaining ≥ 70% of peak torque over a larger range of joint excursion. In conclusion, individuals with a higher flexibility of the hamstrings MTU present a different torque–angle profile, favoring the production of flexion torque toward extended knee positions, displaying larger functional range of motion and a higher mechanical work output during knee flexion.     

Neuromuscular adaptations induced by adjacent joint training

Effects of resistance training are well known to be specific to tasks that are involved during training. However, it remains unclear whether neuromuscular adaptations are induced after adjacent joint training. This study examined the effects of hip flexion training on maximal and explosive knee extension strength and neuromuscular performance of the rectus femoris (RF , hip flexor, and knee extensor) compared with the effects of knee extension training. Thirty‐seven untrained young men were randomly assigned to hip flexion training, knee extension training, or a control group. Participants in the training groups completed 4 weeks of isometric hip flexion or knee extension training. Standardized differences in the mean change between the training groups and control group were interpreted as an effect size, and the substantial effect was assumed to be ≥0.20 of the between‐participant standard deviation at baseline. Both types of training resulted in substantial increases in maximal (hip flexion training group: 6.2% ± 10.1%, effect size = 0.25; knee extension training group: 20.8% ± 9.9%, effect size = 1.11) and explosive isometric knee extension torques and muscle thickness of the RF in the proximal and distal regions. Improvements in strength were accompanied by substantial enhancements in voluntary activation, which was determined using the twitch interpolation technique and RF activation. Differences in training effects on explosive torques and neural variables between the two training groups were trivial. Our findings indicate that hip flexion training results in substantial neuromuscular adaptations during knee extensions similar to those induced by knee extension training.     

Effects of Strength Training on Muscle Development in Prepubescent,Pubescent, and Postpubescent Males

In brief: Thirty-three prepubescent, pubescent, and postpubescent males participated in a nine-week resistive exercise program to test the hypothesis that pubescent males respond better to strength training than older and younger groups do. Before and after the program, the subjects' strength in elbow and knee flexion and extension was tested bilaterally on a dynamometer at two velocities. The posttest showed that all of the subjects gained strength in elbow flexion and extension and knee extension but not in knee flexion. The prepubescent group showed significantly greater gains than the others on three of the 16 tests, but in no case did the pubescent group show significantly greater gains.     

Central and peripheral contributions to fatigue after electrostimulation training

PURPOSE: We examined the effect of 4 (WK4) and 8 wk (WK8) of neuromuscular electrical stimulation (NMES) training on both endurance time and mechanisms contributing to task failure. METHODS: Ten males performed a fatiguing isometric contraction with the knee extensor muscles at 20% of maximal voluntary contraction (MVC) until exhaustion before (B), at WK4, and at WK8 of NMES training. The electromyographic (EMG) activity and muscle activation obtained under MVC were recorded before and after the fatiguing task to assess central fatigue. Torque and EMG responses obtained under electrically evoked contractions were examined before and after the fatiguing task to analyze peripheral fatigue. RESULTS: Knee extensor MVC torque increased significantly between B and WK4 (+16%), between WK4 and WK8 (+10%), and between B and WK8 (+26%), which meant that the average target torque sustained during the fatiguing contraction increased between the testing sessions. Endurance time decreased significantly over the three sessions (493+/-101 s at B, 408+/-159 s at WK4, and 338+/-126 s at WK8) despite a similar reduction in knee extensor MVC (approximately 25%). Negative correlations were found between endurance time absolute changes and target torque absolute gains. Average EMG activity of the knee extensor muscles was lower after training, but the mean rate of increase was similar over the three sessions. Single-twitch contractile properties were not affected by the task. CONCLUSION: We conclude that the endurance time was shorter after 4 and 8 wk of NMES training, and this was associated with higher absolute contraction intensity. Despite endurance time reduction, NMES training did not affect the amount of fatigue at exhaustion nor the central and peripheral contributions to fatigue.