***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Thirty elite tennis players were r and omly assigned to three groups to evaluate shoulder isokinetic internal and external rotation training : an isokinetic concentric group , an isokinetic eccentric group , and a control group with no training . Subjects were tested before and after training both concentrically and eccentrically using an isokinetic dynamometer .  Functional output before and after training was assessed by the average and peak velocity of six maximal serves . The effect of training on serve velocity endurance was also assessed . Statisti cally significant concentric and eccentric strength gains ( 11 % ) were obtained in both training groups when com pared with controls ( decreased total average strain of 2 % ) ( P < 0.0004 ) . Serve velocity increased by greater than 11 % in both training groups , which was a signifi ca nt increase from the average of 1 % in the control group ( P < 0.0001 ) . In the endurance study , training group subjects displayed a tendency to maintain their serve velocity ( loss of approximately 2 % ) greater than controls ( loss of 6.4 % ) ( P < 0.05 ) . Isokinetic training led to increases in objective and functional output in elite tennis players . This training regimen may have signifi cance in the final stages of the rehabilitation of injured shoulders as well as in improved performance and re duced injury risk The purpose of this study was to determine whether cross-education , defined as the increase in strength of an untrained limb after training of the contralateral homologous limb , is specific to low and high velocity eccentric training . Twenty-six subjects were r and omized into two groups ( n=13 each ) that performed unilateral eccentric training of the elbow flexors on an isokinetic dynamometer at velocities of either 30 ° s-1 ( 0.52 rad s-1 ) or 180 ° s-1 ( 3.14 rad s-1 ) . Subjects trained three times per week for 8 weeks . Ten subjects served as controls and did not train . Subjects were tested before and after training for peak torque of the elbow flexors during eccentric and concentric contractions at 30 ° s-1 and 180 ° s-1 . Eccentric peak torque at the velocity of 180 ° s-1 in the untrained arm increased only for the group that trained at that velocity ( P<0.05 ) . There were no other changes in untrained arms for any of the groups at velocities of 30 ° s-1 or 180 ° s-1 . For the trained arm , the increase in eccentric torque ( pooled over velocities ) was greatest for the group training at 180 ° s-1 , whereas the increase in concentric torque was similar for the groups training at 30 ° s-1 and 180 ° s-1 . For the trained arm , there was no specificity for velocity or contraction type . We conclude that cross-education was specific to contraction type and velocity when fast ( but not slow ) eccentric contractions were used during training ; whereas there was no specificity of training in the trained arm O2 uptake ( VO2 ) kinetics and electromyographic ( EMG ) activity from the vastus medialis , rectus femoris , biceps femoris , and medial gastrocnemius muscles were studied during constant-load concentric and eccentric cycling .  Six healthy men performed transitions from baseline to high-intensity eccentric ( HE ) exercise and to high-intensity ( HC ) , moderate-intensity ( MC ) , and low-intensity ( LC ) concentric exercise .  For HE and HC exercise , absolute work rate was equivalent . For HE and LC exercise , VO2 was equivalent . VO2 data were fit by a two- or three-component exponential model . Surface EMG was recorded during the last 12 s of each minute of exercise to obtain integrated EMG and mean power frequency . Only in the HC exercise did VO2 increase progressively with evidence of a slow component ( phase 3 ) , and only in HC exercise was there evidence of a coincident increase with time in integrated EMG of the vastus medialis and rectus femoris muscles ( P < 0.05 ) with no change in mean power frequency . The phase 2 time constant was slower in HC [ 24.0 + /- 1.7 ( SE ) s ] than in HE ( 14.7 + /- 2.8 s ) and LC ( 16.7 + /- 2.2 s ) exercise , while it was not different from MC exercise ( 20.6 + /- 2.1 s ) . These results show that the rate of increase in VO2 at the onset of exercise was not different between HE and LC exercise , where the metabolic dem and was similar , but both had significantly faster kinetics for VO2 than HC exercise . The VO2 slow component might be related to increased muscle activation , which is a function of metabolic dem and and not absolute work rate We compared the effects of concentric ( Con ) and eccentric ( Ecc ) isokinetic training on quadriceps  muscle strength , cross-sectional area , and neural activation .  Women ( age 20.0 + /- 0.5 yr ) r and omly assigned to Con training ( CTG ; n = 16 ) , Ecc training ( ETG ; n = 19 ) , and control ( CG ; n = 19 ) groups were tested before and after 10 wk of unilateral Con or Ecc knee-extension training .  Average torque measured during Con and Ecc maximal voluntary knee extensions  increased 18.4 and 12.8 % for CTG , 6.8 and 36.2 % for ETG , and 4.7 and -1.7 % for CG , respectively . Increases by CTG and ETG were greater than for CG ( P < 0.05 ) . For CTG , the increase was greater when measured with Con than with Ecc testing . For ETG , the increase was greater when measured with Ecc than with Con testing . The increase by ETG with Ecc testing was greater than the increase by CTG with Con testing . Corresponding changes in the integrated voltage from an electromyogram measured during strength testing were 21.7 and 20.0 % for CTG , 7.1 and 16.7 % for ETG , and -8.0 and -9.1 % for CG . Quadriceps cross-sectional area measured by magnetic resonance imaging ( sum of 7 slices ) increased more in ETG ( 6.6 % ) than in CTG ( 5.0 % ) ( P < 0.05 ) . We conclude that Ecc is more effective than Con isokinetic training for developing strength in Ecc isokinetic muscle actions and that Con is more effective than Ecc isokinetic training for developing strength in Con isokinetic muscle actions . Gains in strength consequent to Con and Ecc training are highly dependent on the muscle action used for training and testing . Muscle hypertrophy and neural adaptations contribute to strength increases consequent to both Con and Ecc training The quantification of the progression of  muscle fatigue during a sustained contraction is a valuable tool in several clinical applications , ranging from the evaluation of functional impairment to the development of specific rehabilitative and training protocol s. In these fields , great importance is given to isokinetic contractions . The aim of this paper was twofold : first , to propose signal processing methods for assessing the spectral changes of the surface myoelectric signal due to fatigue during isokinetic concentric and eccentric knee flexion-extension movements at a given angular velocity ( 60/spl deg//s ) ; second , to analyze the electrical manifestations of muscle fatigue of four thigh muscles ( vastus lateralis , vastus medialis , rectus femoris , and biceps femoris ) in the two contraction modalities ( i.e. concentric versus eccentric ) . We demonstrated that , when considering concentric contractions , localized muscle fatigue can be assessed by computing the mean frequency of the frequency marginal of the time-frequency distribution derived from the surface myoelectric signal collected during each contraction cycle . Stronger nonstationarities were observed in the surface myoelectric data recorded within each cyclical movement of the studied eccentric exercise . Thus we propose the computation of the instantaneous mean frequency of the signal based on an original cross-time-frequency algorithm , which proved more sensitive than the frequency marginal in tracking the spectral changes associated with localized muscle fatigue . We derived the average fatigue pattern of the investigated muscles from experimental data recorded from a sample population consisting of twenty healthy subjects and we statistically compared the two contraction modalities . Our results showed that the electrical manifestations of muscle fatigue during concentric contractions were higher than those found during eccentric contractions , although in the latter modality the torque exerted and the mechanical work produced by the subjects were larger than those recorded during the concentric exercise . The results presented in this paper have potential clinical application and they could play an important future role in investigations of muscle behavior during dynamic , highly fatiguing contractions This research was supported by a Duke University Research Council Grant . The purpose of this study was to examine mode and speed specificity of strength training by comparing concentric and eccentric isokinetic exercise of the quadriceps .  Forty-eight healthy men ( mean age = 23.9 years ) were r and omly assigned to one of three groups : concentric training ( C ) , eccentric training ( E ) , or control ( K ) . Average force ( in Newtons ) of 3 concentric and of 3 eccentric quadriceps contractions on the KIN-COM(R ) dynamometer at 60 , 120 , and 180 degrees /sec was evaluated prior to and following a 6 week period during which only the C and E groups trained . Training sessions ( 3/week ) included 4 submaximal and 1 maximal warm-up followed by 10 maximal effort isokinetic contractions of the quadriceps at 120 degrees /sec for each leg . Group C subjects trained concentrically only while Group E subjects trained eccentrically only . A t-test for independent means showed no significant right/left differences . ANOVA and Scheffe 's F-tests were then used to assess the differences in training effects among the 3 groups for the left leg only . Results showed that although Group C increased slightly in both concentric and eccentric force at all speeds , the gains were significant only for concentric force at 180 degrees /sec . Group E showed significant gains ( p < 0.05 ) in eccentric force at all speeds but not in concentric force . The K group had no significant change in concentric or eccentric force at any speed . We conclude that the eccentric mode of isokinetic exercise has highly specific strength training effects while the concentric mode has less specific training effects . In addition , speed of exercise does not appear to have specific training effects . J Orthop Sports Phys Ther 1989;11(2):70 - 75 The purpose of this study was to compare the short-term strength and neural adaptations to eccentric and concentric training at equal force levels . Forty-two sedentary women ( age = 21.5 yr ) were ranked based on the initial quadriceps strength score , and trios of subjects were r and omly assigned to either an eccentric ( n = 14 ) , a concentric ( n = 14 ) , or a nonexercising control group ( n = 14 ) . Training involved a total of 824 eccentric or concentric quadriceps actions at 1.05 rad.s-1 administered in four sets of 6 - 10 repetitions , four times per week for 6 wk . Before and after training , all subjects were tested for unilateral maximal isometric and eccentric and concentric actions at 1.05 rad.s-1 and for a 40-repetition eccentric and concentric fatigue series of the left and right quadriceps . Surface electromyographic activity of the vastus lateralis and medialis was monitored during testing . Concentric training increased concentric ( 36 % , P < 0.05 ) , isometric ( 18 % , P < 0.05 ) , and eccentric strength ( 13 % ) , and eccentric training increased eccentric ( 42 % , P < 0.05 ) , isometric ( 30 % , P < 0.05 ) , and concentric ( 13 % ) strength . Eccentric training improved eccentric and isometric strength more ( P < 0.05 ) than did concentric training . The electromyographic adaptations were greater with eccentric training . Cross-education was 6 % , and neither training mode modified fatigability . The data suggest that training of the quadriceps muscle with submaximal eccentric actions brings about greater strength adaptations faster than does training with maximal-level concentric actions in women . This greater adaptation is likely to be mediated by both mechanical and neural factors The purpose of this study was to estimate the efficiency of ATP utilization  for concentric , eccentric , and isometric muscle action in the human tibialis anterior and extensor digitorum longus in vivo . A dynamometer was used to quantitate muscle work , or tension , while simultaneous 31P-nuclear magnetic resonance data were collected to monitor ATP , phosphocreatine , inorganic phosphate , and pH. The relative efficiency of the actions was estimated in two ways : steady-state effects on high-energy phosphates and a direct comparison of ATP synthesis rates with work . In the steady state , the cytosolic free energy dropped to the lowest value with concentric activity , followed by eccentric and isometric action for comparative muscle tensions . Estimates of ATP synthesis rates revealed a mechanochemical efficiency [ i.e. , ATP production rate/work ( both in J/s ) ] of 15.0 + /- 1.3 % in concentric and 34.7 + /- 6.1 % in eccentric activity . The estimated maximum ATP production rate was highest in concentric action , suggesting an activation of energy metabolism under these conditions . By using direct measures of metabolic strain and ATP turnover , these data demonstrate a decreasing metabolic efficiency in human muscle action from isometric , to eccentric , to concentric action The objectives of this study were to determine whether the occurrence of  delayed onset muscle soreness ( DOMS )  for the vastus lateralis muscle was associated with elevated intramuscular pressure ( IMP ) ; and to assess , whether high eccentric forces occurred at an increased muscle length ( as determined by joint angle ) . Therefore 
    Output:
    
Meta-analyses showed that when eccentric exercise was performed at higher intensities compared with concentric training , total strength and eccentric strength increased more significantly .
However , compared with concentric training , strength gains after eccentric training appeared more specific in terms of velocity and mode of contraction .
Eccentric training performed at high intensities was shown to be more effective in promoting increases in muscle mass measured as muscle girth .
In addition , eccentric training also showed a trend towards increased muscle cross-sectional area measured with magnetic resonance imaging or computerised tomography .
Subgroup analyses suggest that the superiority of eccentric training to increase muscle strength and mass appears to be related to the higher loads developed during eccentric contractions .
The specialised neural pattern of eccentric actions possibly explains the high specificity of strength gains after eccentric training .