Specificity of velocity in strength training

Twenty-one male volunteers (ages 23-25 years) were tested pre- and post training for maximal knee extension power at five specific speeds (1.05, 2.09, 3.14, 4.19, and 5.24 rad X s-1) with an isokinetic dynamometer. Subjects were assigned randomly to one of three experimental groups; group S, training at 1.05 rad X s-1 (n = 8), group I, training at 3.14 rad X s-1 (n = 8) or group F, training at 5.24 rad X s-1 (n = 5). Subjects trained the knee extensors by performing 10 maximal voluntary efforts in group S, 30 in group I and 50 in group F six times a week for 8 weeks. Though group S showed significant increases in power at all test speeds, the percent increment decreased with test speed from 24.8% at 1.05 rad X s-1 to 8.6% at 5.24 rad X s-1. Group I showed almost similar increment in power (18.5-22.4 at all test speeds except at 2.09 rad X s-1 (15.4%). On the other hand, group F enhanced power only at faster test speeds (23.9% at 4.19 rad X s-1 and 22.8% at 5.24 rad X s-1).     

Relationship between work and electromyographic activity during repeated leg muscle contractions in orienteers

Contraction work (CW) was recorded for each of 200 repetitive isokinetic plantar flexions (1.05 rad.s-1) and knee extensions (1.57 rad.s-1) in 14 elite male orienteers. Simultaneous recordings of integrated electromyograms (iEMG) were obtained from the 3 parts of triceps surae and from 3 superficial portions of quadriceps femoris. CW in both muscle groups decreased significantly during the first 30 contractions (the fatigue phase), followed by a steady state level. The relative steady state level was higher for the plantar flexors (70 +/- 17%) than for the knee extensors (56 +/- 12%). For quadriceps a significant increase in iEMG occurred during the first 10 contractions followed by a decrease, whereas the iEMG of the plantar flexors showed a gradual decrease to the steady state level, which was similar for the two muscle groups (71-72%). The chosen expression of output/input balance (CW/iEMG) was constant throughout the plantarflexion test but decreased during the initial 20 knee extensions down to 82%. Thus, the fatigue phase of the knee extensions appeared to be divided into two; the first part had decreases in both CW and CW/iEMG and the second part with a decrease in CW alone. In contrast the plantar flexors only showed the characteristics of the second part.     

The effect of range of motion and isometric pre-activation on isokinetic torques

The effect of an increased angle of excursion and isometric pre-activation on isokinetic torques of knee extensors was investigated in five male subjects, mean age 35.0 years, SD 9.6. Peak torque and isoangular torque at 0.52 rad from full knee extension (FKE) were measured when contractions were carried out at 3.14, 4.19 and 5.24 rad.s-1 starting: 1) from a standard knee angle (SA) of 1.57 rad from FKE, 2) from the same starting angle as SA, plus an isometric preload (P) equivalent to 25% of isometric maximal voluntary contraction and 3) from an increased angle of knee flexion (IA), 2.09 rad from FKE plus P. Surface integrated electromyograms (iEMG) of the vastus lateralis muscle in SA and IA + P were also recorded. The IA + P had the effect of increasing peak torque, as compared to SA, on average by 12.0%, SD 7.5% (P less than 0.001) at 3.14 rad.s-1, 19.5%, SD 5.5% (P less than 0.001) at 4.19 rad.s-1, 21.6%, SD 10.7% (P less than 0.001) at 5.24 rad.s-1 and of increasing mean iEMG by 15.7%, SD 7.0% (P less than 0.001) at 5.24 rad.s-1. The IA + P also had the effect of increasing the angle from FKE at which peak torque occurred: from means of 0.80 rad, SD 0.11 to 1.00 rad, SD 0.07 at 3.14 rad.s-1, from 0.65 rad, SD 0.11 to 0.92 rad, SD 0.09 at 4.19 rad.s-1 and from 0.60 rad, SD 0.11 to 0.88 rad, SD 0.11 at 5.24 rad.s-1 (P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of isokinetic training of the knee extensors on isometric strength and peak power output during cycling

Isokinetic training of right and left quadriceps femoris was undertaken three times per week for 16 weeks. One group of subjects (n = 13) trained at an angular velocity of 4.19 rad.s-1 and a second group (n = 10) at 1.05 rad.s-1. A control group (n = 10) performed no training. Maximal voluntary contraction (MVC) of the quadriceps, and peak pedal velocity nu p,peak) and peak power output (Wpeak) during all-out cycling (against loads equivalent to 9, 10, 11, 12, 13 and 14% MVC) were assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of the performance variables (P > 0.05). No significant difference in MVC was observed for any group after the 16-week period (P = 0.167). The post-training increases in average Wpeak (7%) and nu p,peak (6%) during the cycle tests were each significantly different from the control group response (P = 0.018 and P = 0.008, respectively). It is concluded that 16 weeks of isokinetic strength training of the knee extensors is able to significantly improve nu p, peak and Wpeak during spring cycling, an activity which demands considerable involvement of the trained muscle group but with its own distinct pattern of coordination.     

Isokinetic rehabilitation after arthroscopic meniscectomy.

The aim of this study was to assess the effects in humans of early (2 weeks) and delayed (6 weeks) isokinetic strength training in the recovery of muscle strength following an arthroscopic partial meniscectomy. The peak torque developed in the quadriceps and hamstrings and the torque developed at a knee angle of 1.05 rad were evaluated in 16 subjects, pre-operatively (pre-op), and 2, 6, and 10 weeks post-operatively (post-op), on an isokinetic device at four different velocities (1.05, 2.09, 3.14, and 4.19 rad.s-1). The fatigue characteristics of the muscles were evaluated by having the subject perform 15 maximal contractions at 3.14 rad.s-1. Training was done on the same device (three times a week for 1-2 months), beginning either 2 or 6 weeks post-op. A repeated measures analysis of variance demonstrated a time effect but no differences between groups and no interactions. Torques developed by the knee flexors and extensors were significantly smaller 2 weeks post-op than pre-op, at all velocities tested. Torques developed in the quadriceps recovered to their pre-op values by 6 weeks, and further gained significantly in strength from 6 to 10 weeks. Quadriceps torques remained weaker than the contralateral side at 10 weeks. Hamstrings torques were either higher or similar to pre-op values by 6 weeks, and demonstrated increases from 6 to 10 weeks post-op at 1.05 and 4.19 rad.s-1 only. Total work and average power developed by the quadriceps and hamstrings during the fatigue protocol changed with time in a similar manner to torque.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hemodynamics and O2 uptake during maximal knee extensor exercise in untrained and trained human quadriceps muscle: effects of hyperoxia.

To elucidate the potential limitations on maximal human quadriceps O2 capacity, six subjects trained (T) one quadriceps on the single-legged knee extensor ergometer (1 h/day at 70% maximum workload for 5 days/wk), while their contralateral quadriceps remained untrained (UT). Following 5 wk of training, subjects underwent incremental knee extensor tests under normoxic (inspired O2 fraction = 21%) and hyperoxic (inspired O2 fraction = 60%) conditions with the T and UT quadriceps. Training increased quadriceps muscle mass (2.9 +/- 0.2 to 3.1 +/- 0.2 kg), but did not change fiber-type composition or capillary density. The T quadriceps performed at a greater peak power output than UT, under both normoxia (101 +/- 10 vs. 80 +/- 7 W; P < 0.05) and hyperoxia (97 +/- 11 vs. 81 +/- 7 W; P < 0.05) without further increases with hyperoxia. Similarly, thigh peak O2 consumption, blood flow, vascular conductance, and O2 delivery were greater in the T vs. the UT thigh (1.4 +/- 0.2 vs. 1.1 +/- 0.1 l/min, 8.4 +/- 0.8 vs. 7.2 +/- 0.8 l/min, 42 +/- 6 vs. 35 +/- 4 ml x min(-1) x mmHg(-1), 1.71 +/- 0.18 vs. 1.51 +/- 0.15 l/min, respectively) but were not enhanced with hyperoxia. Oxygen extraction was elevated in the T vs. the UT thigh, whereas arteriovenous O2 difference tended to be higher (78 +/- 2 vs. 72 +/- 4%, P < 0.05; 160 +/- 8 vs. 154 +/- 11 ml/l, respectively; P = 0.098) but again were unaltered with hyperoxia. In conclusion, the present results demonstrate that the increase in quadriceps muscle O2 uptake with training is largely associated with increases in blood flow and O2 delivery, with smaller contribution from increases in O2 extraction. Furthermore, the elevation in peak muscle blood flow and vascular conductance with endurance training seems to be related to an enhanced vasodilatory capacity of the vasculature perfusing the quadriceps muscle that is unaltered by moderate hyperoxia.     

Throwing performance after resistance training and detraining

The purpose of the present study was to investigate the effect of short-term resistance training and detraining on shot put throwing performance. Eleven young healthy subjects with basic shot put skills participated in 14 weeks of resistance training, which was followed by 4 weeks of detraining. Shot put performance in four field tests was measured before (T1) and after (T2) resistance training and after detraining (T3). At the same time points, one repetition maximum (1RM) was measured in squat, bench press, and leg press. Fat-free mass (FFM) was determined with dual x-ray absorptiometry and muscle biopsies obtained from vastus lateralis for the determination of fiber type composition and cross-sectional area (CSA). 1RM strength increased 22-34% (p < 0.01) at T2 and decreased 4-5% (not significantly different) at T3. Shot put performance increased 6-12% (p < 0.05) after training and remained unaltered after detraining. FFM increased at T2 (p < 0.05) but remained unchanged between T2 and T3. Muscle fiber CSA increased 12-18% (p < 0.05) at T2. Type I muscle fiber CSA was not altered after detraining, but type IIa and IIx fiber CSA was reduced 10-12% (p < 0.05). The percentage of type IIx muscle fibers was reduced after training (T1 = 18.7 +/- 4, T2 = 10.4 +/- 1; p < 0.05), and it was increased at T3 compared with T2 (T3 = 13.7 +/- 1; p < 0.05). These results suggest that shot put performance remains unaltered after 4 weeks of complete detraining in moderately resistance-trained subjects. This might be linked to the concomitant reduction of muscle fiber CSA and increase in the percentage of type IIx muscle fibers.     

Muscle cross-sectional area and torque in resistance-trained subjects

Eight elite male bodybuilders (MB), five elite female bodybuilders (FB), eight male control (MC), and eight female control recreational weight-trainers (FC) performed maximal elbow flexions on an isokinetic dynamometer at velocities between 1.02 and 5.24 rad.s-1, from which peak torque (PT) was measured. Elbow flexor cross-sectional area (CSA) was measured by computed tomographic scanning. Flexor CSA.lean body mass-1 ratios were greater in MB than in other subject groups. Correlations of PT were positively related to CSA but negatively to CSA.lean body mass-1 and to PT.CSA-1. PT.CSA-1 at low-velocity contractions were greater in MC and FC than in MB and FB groups, suggesting a training effect. The velocity-associated declines in torque between velocities of 1.02 and 5.24 rad.s-1 averaged 28.4 +/- 0.9% and were statistically identical in men and women among the subject groups, suggesting that neither gender nor training had affected this variable.     

Early skeletal muscle hypertrophy and architectural changes in response to high-intensity resistance training.

The onset of whole muscle hypertrophy in response to overloading is poorly documented. The purpose of this study was to assess the early changes in muscle size and architecture during a 35-day high-intensity resistance training (RT) program. Seven young healthy volunteers performed bilateral leg extension three times per week on a gravity-independent flywheel ergometer. Cross-sectional area (CSA) in the central (C) and distal (D) regions of the quadriceps femoris (QF), muscle architecture, maximal voluntary contraction (MVC), and electromyographic (EMG) activity were measured before and after 10, 20, and 35 days of RT. By the end of the training period, MVC and EMG activity increased by 38.9 +/- 5.7 and 34.8% +/- 4.7%, respectively. Significant increase in QF CSA (3.5 and 5.2% in the C and D regions, respectively) was observed after 20 days of training, along with a 2.4 +/- 0.7% increase in fascicle length from the 10th day of training. By the end of the 35-day training period, the total increase in QF CSA for regions C and D was 6.5 +/- 1.1 and 7.4 +/- 0.8%, respectively, and fascicle length and pennation angle increased by 9.9 +/- 1.2 and 7.7 +/- 1.3%, respectively. The results show for the first time that changes in muscle size are detectable after only 3 wk of RT and that remodeling of muscle architecture precedes gains in muscle CSA. Muscle hypertrophy seems to contribute to strength gains earlier than previously reported; flywheel training seems particularly effective for inducing these early structural adaptations.     

Changes in voluntary and electrically induced contractions during strength training and detraining

To elucidate the changes in neuro-muscular function during strength training and detraining, five male subjects underwent progressive isotonic strength training of their calf muscles three times a week for 8 weeks with additional detraining for the same periods. Electrically evoked twitch contractions were induced in the triceps surae muscles of each subject every 4 weeks during the training and detraining periods. At the same time, maximal voluntary isometric contractions (MVC) and the maximal girth of the calf (MGC) were measured. During the training period, MVC increased significantly from 98.4 to 129.6 Nm (31.7%, P less than 0.01) for the first 4 weeks of training but MGC showed little increase. Neither of the changes correlated with each other. Twitch contraction parameters, i.e. maximal twitch torque (Pt), maximal rate of torque development (max dT/dt) and rate of relaxation (relax dT/dt) showed no statistical change. During detraining, on the contrary, a large and significant increase (22.5%, P less than 0.01) was observed in max dT/dt without any changes in Pt and relax dT/dt. The MVC/Pt showed both significant increases during training and decreases during detraining. Our data suggest that short term strength training as employed in the present study does not induce changes in the contractile properties of the muscle during training, but may significantly affect the rate of force development during the subsequent detraining period, indicating the possible existence of complex post-training muscle adaptation.     

Reproducibility of isokinetic leg strength and endurance characteristics of adult men and women

Day-to-day variability and single-measurement reliability of selected isokinetic knee extension-flexion strength and endurance indices were assessed in 10 adult men and 8 adult women. On three occasions separated by at least 5 days, the subjects completed 4 reciprocal maximal voluntary contractions (MVC) at different angular velocities (1.05 rad.s-1 and 3.14 rad.s-1). The men also completed a muscular endurance test consisting of 30 reciprocal, MVC at 3.14 rad.s-1. Coefficient of variation, intra-class correlation coefficient and standard error of single-measurement scores support the continued use of gravity corrected peak torque (PT) and average peak torque (APT) as indices of isokinetic leg strength. Similarly, gravity corrected APT and total work should be the recommended indices of isokinetic leg muscular endurance in men. The results suggest that these isokinetic indices must be assessed using multiple day-to-day trial protocols adequately to describe performance capacity. Composite indices such as the ratio of Knee flexion to extension PT and fatigue measurements offer considerably reduced reliability and a greater potential for misinterpretation. The reliability of knee extension indices generally exceeds that of flexion indices. Similar variability and reproducibility of responses were observed between men and women and between reciprocal contractions performed at angular velocities of 1.05 rad.s-1 and 3.14 rad.s-1.     

Incompatibility of endurance- and strength-training modes of exercise

Twenty-two male and female subjects trained for 7 wk for endurance (group E), for strength (group IS), or for both strength and endurance (group C) to evaluate the effect of concurrent performance of both modes of training on the in vivo force-velocity relationship of human muscle and on aerobic power. Endurance training consisted of five 5-min sessions three times a week on cycle ergometer with a work load that approached the subject's peak cycle-ergometer O2 uptake (peak CE VO2). Strength training consisted of two 30-s sets of maximal knee extensions per day performed on an isokinetic dynamometer three times a week at a velocity of 4.19 rad X s-1. Group C performed the same training as groups IS and E, alternating days of strength and endurance training. Subjects (groups C and IS) were tested pre- and posttraining for maximal knee-extension torque at a specific joint angle (0.52 rad below horizontal) for seven specific angular velocities (0, 0.84, 1.68, 2.81, 3.35, 4.19, and 5.03 rad X s-1). Groups C and E were tested for peak CE VO2 pretraining, at 14-day intervals, and posttraining. Group IS showed significant increases in angle-specific maximal torque at velocities up to and including the training speed (4.19 rad X s-1). Group C showed increases (P less than 0.05) at velocities of 0, 0.84, and 1.68 rad X s-1 only. Peak CE VO2, when expressed in relative or absolute terms, increased (P less than 0.05) approximately 18% for both groups E and C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of isometric training on the elasticity of human tendon structures in vivo.

The present study aimed to investigate the effect of isometric training on the elasticity of human tendon structures. Eight subjects completed 12 wk (4 days/wk) of isometric training that consisted of unilateral knee extension at 70% of maximal voluntary contraction (MVC) for 20 s per set (4 sets/day). Before and after training, the elongation of the tendon structures in the vastus lateralis muscle was directly measured using ultrasonography while the subjects performed ramp isometric knee extension up to MVC. The relationship between the estimated muscle force and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness of the tendon structures. The training increased significantly the volume (7.6+/-4.3%) and MVC torque (33.9+/-14.4%) of quadriceps femoris muscle. The L values at force production levels beyond 550 N were significantly shorter after training. The stiffness increased significantly from 67.5+/-21.3 to 106.2+/-33.4 N/mm. Furthermore, the training significantly increased the rate of torque development (35.8 +/- 20.4%) and decreased electromechanical delay (-18.4+/-3.8%). Thus the present results indicate that isometric training increases the stiffness and Young's modulus of human tendon structures as well as muscle strength and size. This change in the tendon structures would be assumed to be an advantage for increasing the rate of torque development and shortening the electromechanical delay.     

Effects of velocity of isokinetic training on strength, power, and quadriceps muscle fibre characteristics

Twenty young men trained the right knee extensors and flexors on an isokinetic dynamometer three times weekly over a 10-week period. During each session, 10 men in the slow training group completed three sets of 8 maximal contractions at a rate of 1.05 rad s-1, whereas the other 10, the fast group, completed three sets of 20 contractions at a rate of 4.19 rad s-1. Subjects wer pre- and post-tested for peak torque and power on an isokinetic dynamometer at 1.05, 3.14, and 4.19 rad s-1. Proportions of muscle fibre-types and fibre cross-sectional areas were determined from biopsy specimens taken before and after training from the right vastus lateralis. When testing was conducted at 1.05 rad s-1, the slow group improved (P less than 0.05) peak torque by 24.5 N m (8.5%), but no change was noted for the fast group. Power increased (P less than 0.05) by 32.7 W (13.6%) in the slow group and 5.5 W (2.5%) in the fast. At 3.14 rad s-1, both groups increased (P less than 0.05) peak torque and power. At 4.19 rad s-1, the fast group increased (P less than 0.05) peak torque by 30.0 N m (19.7%), whereas no training effect was observed in the slow group. There was no significant change in power in either group at 4.19 rad s-1. No significant changes were observed over the 10-week training period in percentages of type I, IIa and IIb fibres, but both groups showed significant increases (P less than 0.05) in type I and IIa fibre areas.(ABSTRACT TRUNCATED AT 250 WORDS)     

Eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man

The primary purpose of this investigation was to study the eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man using a recently developed combined isometric, concentric and eccentric controlled velocity dynamometer (the SPARK System). A secondary purpose was to compare the method error associated with maximal voluntary concentric and eccentric torque output over a range of testing velocities. 21 males (21-32 years) performed on two separate days maximal voluntary isometric, concentric and eccentric contractions of the quadriceps femoris at 4 isokinetic lever arm velocities of 0 degree.s-1 (isometric), 30 degrees.s-1, 120 degrees.s-1 and 270 degrees.s-1. Eccentric peak torque and angle-specific torques (measured every 10 degrees from 30 degrees to 70 degrees) did not significantly change from 0 degrees.s-1 to 270 degrees.s-1 (p greater than 0.005) with the exception of angle-specific 40 degrees torque, which significantly increased; p less than 0.05). The mean method error was significantly higher for the eccentric tests (10.6% +/- 1.6%) than for the concentric tests (8.1% +/- 1.7%) (p less than 0.05). The mean method error decreased slightly with increasing concentric velocity (p greater than 0.05), and increased slightly with increasing eccentric velocity (p greater than 0.05). A tension restricting neural mechanism, if active during maximal eccentric contractions, could possibly account for the large difference seen between the present eccentric torque-velocity results and the classic results obtained from isolated animal muscle.     

Changes in the human muscle force-velocity relationship in response to resistance training and subsequent detraining.

Previous studies show that cessation of resistance training, commonly known as "detraining," is associated with strength loss, decreased neural drive, and muscular atrophy. Detraining may also increase the expression of fast muscle myosin heavy chain (MHC) isoforms. The present study examined the effect of detraining subsequent to resistance training on contractile performance during slow-to-medium velocity isokinetic muscle contraction vs. performance of maximal velocity "unloaded" limb movement (i.e., no external loading of the limb). Maximal knee extensor strength was measured in an isokinetic dynamometer at 30 and 240 degrees/s, and performance of maximal velocity limb movement was measured with a goniometer during maximal unloaded knee extension. Muscle cross-sectional area was determined with MRI. Electromyographic signals were measured in the quadriceps and hamstring muscles. Twitch contractions were evoked in the passive vastus lateralis muscle. MHC isoform composition was determined with SDS-PAGE. Isokinetic muscle strength increased 18% (P < 0.01) and 10% (P < 0.05) at slow and medium velocities, respectively, along with gains in muscle cross-sectional area and increased electromyogram in response to 3 mo of resistance training. After 3 mo of detraining these gains were lost, whereas in contrast maximal unloaded knee extension velocity and power increased 14% (P < 0.05) and 44% (P < 0.05), respectively. Additionally, faster muscle twitch contractile properties along with an increased and decreased amount of MHC type II and MHC type I isoforms, respectively, were observed. In conclusion, detraining subsequent to resistance training increases maximal unloaded movement speed and power in previously untrained subjects. A phenotypic shift toward faster muscle MHC isoforms (I --> IIA --> IIX) and faster electrically evoked muscle contractile properties in response to detraining may explain the present results.     

Fatigue depresses maximal in vitro skeletal muscle Na(+)-K(+)-ATPase activity in untrained and trained individuals.

This study investigated whether fatiguing dynamic exercise depresses maximal in vitro Na(+)-K(+)-ATPase activity and whether any depression is attenuated with chronic training. Eight untrained (UT), eight resistance-trained (RT), and eight endurance-trained (ET) subjects performed a quadriceps fatigue test, comprising 50 maximal isokinetic contractions (180 degrees /s, 0.5 Hz). Muscle biopsies (vastus lateralis) were taken before and immediately after exercise and were analyzed for maximal in vitro Na(+)-K(+)-ATPase (K(+)-stimulated 3-O-methylfluoroscein phosphatase) activity. Resting samples were analyzed for [(3)H]ouabain binding site content, which was 16.6 and 18.3% higher (P < 0.05) in ET than RT and UT, respectively (UT 311 +/- 41, RT 302 +/- 52, ET 357 +/- 29 pmol/g wet wt). 3-O-methylfluoroscein phosphatase activity was depressed at fatigue by -13.8 +/- 4.1% (P < 0.05), with no differences between groups (UT -13 +/- 4, RT -9 +/- 6, ET -22 +/- 6%). During incremental exercise, ET had a lower ratio of rise in plasma K(+) concentration to work than UT (P < 0.05) and tended (P = 0.09) to be lower than RT (UT 18.5 +/- 2.3, RT 16.2 +/- 2.2, ET 11.8 +/- 0.4 nmol. l(-1). J(-1)). In conclusion, maximal in vitro Na(+)-K(+)-ATPase activity was depressed with fatigue, regardless of training state, suggesting that this may be an important determinant of fatigue.     

Muscle morphological and strength adaptations to endurance vs. resistance training

Fascicle angle (FA) is suggested to increase as a result of fiber hypertrophy and furthermore to serve as the explanatory link in the discrepancy in the relative adaptations in the anatomical cross-sectional area (CSA) and fiber CSA after resistance training (RT). In contrast to RT, the effects of endurance training on FA are unclear. The purpose of this study was therefore to investigate and compare the longitudinal effects of either progressive endurance training (END, n = 7) or RT (n = 7) in young untrained men on FA, anatomical CSA, and fiber CSA. Muscle morphological measures included the assessment of vastus lateralis FA obtained by ultrasonography and anatomical CSA by magnetic resonance imaging of the thigh and fiber CSA deduced from histochemical analyses of biopsy samples from m. vastus lateralis. Functional performance measures included VO2max and maximal voluntary contraction (MVC). The RT produced increases in FA by 23 ± 8% (p < 0.01), anatomical CSA of the knee extensor muscles by 9 ± 3% (p = 0.001), and fiber CSA by 19 ± 7% (p < 0.05). RT increased knee extensor MVC by 20 ± 5% (p < 0.001). END increased VO2max by 10 ± 2% but did not evoke changes in FA, anatomical CSA, or in fiber CSA. In conclusion, the morphological changes induced by 10 weeks of RT support that FA does indeed serve as the explanatory link in the observed discrepancy between the changes in anatomical and fiber CSA. Contrarily, 10 weeks of endurance training did not induce changes in FA, but the lack of morphological changes from END indirectly support the fact that fiber hypertrophy and FA are interrelated.     

Adaptations in coactivation after isometric resistance training.

Twenty sedentary male university students were randomly assigned to an experimental or a control group. The experimental group trained the knee extensors of one leg by producing 30 isometric extension maximal voluntary contractions (MVC) per day, three times per week for 8 wk. After 8 wk of training, extensor MVC in the trained leg increased 32.8% (P less than 0.05), but there was no change in vastus lateralis maximal integrated electromyographic activity (IEMGmax). The most important finding was that the degree of hamstring coactivation during extension MVC decreased by approximately 20% (P less than 0.05) after the 1st wk of training. Less pronounced adaptations occurred in the untrained leg: extension MVC force increased 16.2% (P less than 0.05), hamstring coactivity decreased 13% (P less than 0.05) after 2 wk of training, and vastus lateralis IEMGmax was unchanged. The same measures in legs of the control group were not changed during the study. There were no changes in flexion MVC, biceps femoris IEMGmax, or the degree of quadriceps coactivity during flexion MVC in either leg of the control or experimental group. A reduction in hamstring coactivity in the trained and untrained legs indicates that these muscles provide less opposing force to the contracting quadriceps. We conclude that this small but significant decrease in hamstring coactivation that occurs during the early stages of training is a nonhypertrophic adaptation of the neuromuscular system in response to static resistance training of this type.     

The relationship between contraction and relaxation during fatiguing isokinetic shoulder flexions. An electromyographic study

Knowledge of the strength, endurance and coordination of the shoulder muscles during dynamic contractions in healthy women would contribute to the understanding of symptoms in that part of the body in patients with myalgia. Twenty clinically healthy women performed single maximal forward shoulder flexions at four different angular velocities (0.57-3.14 rad.s-1). The same subjects also took part in two endurance tests (at angular velocities of 0.57 and 2.09 rad.s-1, respectively) consisting of 150 repeated maximal shoulder flexions. Electromyographic activity (EMG) was registered from four shoulder flexors using surface electrodes. Work was used as the mechanical variable. During the endurance tests subjects rated their perception of fatigue in the shoulder muscles. Work and the amplitude of the EMG signals decreaesd with angular velocity. The mean power frequency of the EMG was constant in the span of angular velocities investigated. During the endurance tests, work and the mean power frequency decreased during the initial 40-60 contractions followed by stable levels. The relative work level was higher at 2.09 than at 0.57 rad.s-1. Greater relative increases of the signal amplitudes of EMG occurred at 2.09 than at 0.57 rad.s-1. The EMG activity between the flexions (during the supposed passive extension) was higher at 2.09 than at 0.57 rad.s-1. Such a high activity was associated with a low mechanical performance at 2.09 rad.s-1. It is suggested that the initial sharp decreases in work and in mean power frequency reflect the fatiguing of the fast twitch motor units. Dynamic work consisting of continuous activity could predispose to muscle complaints.