Twenty-Four Months' Resistance and Endurance Training Improves Muscle Size and Physical Functions but Not Muscle Quality in Older Adults Requiring Long-Term Care.

OBJECTIVES: To assess the effects of 24 months training on muscle quality, size, strength, and gait abilities in older adults who need long-term care. DESIGN: Non-randomized controlled trial Setting: Kawai Rehabilitation Center and Kajinoki Medical Clinic. PARTICIPANTS: Ten older participants who needed long-term care (age, 76.7 ± 5.6 years) were participated as training group (Tr-group) and 10 older men and women who did not require long-term care (age, 72.9 ± 6.6 years) comprised the control group (Cont-group). INTERVENTION: Tr-group performed resistive and endurance exercises once or twice a week for 24 months. MEASUREMENTS: Using ultrasound images, echo intensity (EI) and muscle thickness were measured in the rectus femoris and biceps femoris as an index of muscle quality and size. Physical performance was measured before and after the training; performance parameters included knee extension peak torque, 5-m normal and maximal walk test, sit-to-stand and timed up and go test. RESULTS: After the training, there was no change in EI, while BF thickness was increased (pre; 1.82 ± 0.29 cm, 24 months; 2.14 ± 0.23 cm, p < 0.05) in Tr-group. Walk-related performances were improved after the training in Tr-group (i.e. 5-m walk test and timed up and go test). The percent change of knee extension peak torque explained the percent change of EI in the rectus femoris (regression coefficient = 1.24, R = 0.91, adjusted R2 = 0.82, p < 0.001). CONCLUSIONS: Twenty-four months' training induced muscle hypertrophy and improved physical functions. Increased muscle quality in the rectus femoris could be a key to improved knee extension peak torque, with the potential to eventually reduce the need for long-term care in older individuals.

Vastus intermedius vs vastus lateralis fascicle behaviors during maximal concentric and eccentric contractions.

Vastus intermedius (VI) plays a major role in knee extension, but its fascicle behaviors during dynamic contractions are not well understood. This study aimed to compare VI and vastus lateralis (VL) fascicle behaviors during singular maximal concentric and eccentric contractions. Thirteen men (27.1 ± 3.4 years) performed maximal isokinetic concentric contractions through knee joint angles of 105° to 35° (0° = full extension) and eccentric contractions from 35° to 105° at an angular velocity of 30°/s. Longitudinal VI and VL sonographic images were simultaneously recorded at 30 Hz, and muscle fascicle lengths at the knee joint angles of 40° and 100° were measured to compare the magnitudes of fascicle length change between the muscles. During concentric contractions, VI and VL fascicle lengths at 100° were 108 ± 12 mm and 104 ± 12 mm, respectively, and shortened by 36 ± 12 mm for VI and 28 ± 13 mm for VL (not statistically different; P = .13) at 40°. During eccentric contractions, VI and VL fascicle lengths at 40° were 72 ± 7 mm and 75 ± 8 mm, respectively, but lengthened by 35 ± 9 mm for VI and 24 ± 5 mm for VL at 100°, with a significant difference between the muscles (P = .01). These results indicate that VI fascicles are lengthened 1.4 times more than VL fascicles during eccentric contractions, whereas VI and VL fascicles shorten similarly during concentric contractions. This suggests a possibility that a greater mechanical strain is imposed to VI than VL during eccentric contractions.

Effect of knee joint angle on neuromuscular activation of the vastus intermedius muscle during isometric contraction.

The purpose of this study was to compare the relationship between surface electromyography (EMG) and knee joint angle of the vastus intermedius muscle (VI) with the synergistic muscles in the quadriceps femoris (QF) muscle group. Fourteen healthy men performed maximal voluntary contractions during isometric knee extension at four knee joint angles from 90°, 115°, 140°, and 165° (180° being full extension). During the contractions, surface EMG was recorded at four muscle components of the QF muscle group: the VI, vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles. The root mean square of the surface EMG at each knee joint angle was calculated and normalized by that at a knee joint angle of 90° for individual muscles. The normalized RMS of the VI muscle was significantly lower than those of the VL and RF muscles at the knee joint angles of 115° and 165° and those of the VL, VM, and RF muscles at the knee joint angle of 140° (P<0.05). The present results suggest that the neuromuscular activation of the VI muscle is regulated in a manner different from the alteration of the knee joint angle compared with other muscle components of the QF muscle group.

Effects of deconditioning on the initial ventilatory and circulatory responses at the onset of exercise in man.

In order to elucidate the effects of deconditioning (inactivity) on the ventilatory and circulatory responses at the onset of exercise within 20 s, we initiated head-down bed rest and unilateral lower limb suspension experiments, and measured these responses to dynamic voluntary leg exercise and passive movements. Initial ventilatory and heart rate responses to voluntary exercise were attenuated after bed rest but showed no change after suspension or during passive movements, suggesting the minimal role of peripheral neural reflex.

The adaptive responses in several mediators linked with hypertrophy and atrophy of skeletal muscle after lower limb unloading in humans.

AIM: To determine the adaptive changes in several molecules regulating muscle hypertrophy and atrophy after unloading, we examined whether unilateral lower limb suspension changes the mRNA and protein levels of SRF-linked (RhoA, RhoGDI, STARS and SRF), myostatin-linked (myostatin, Smad2, Smad3 and FLRG) and Foxo-linked (P-Akt, Foxo1, Foxo3a and Atrogin-1) mediators. METHODS: A single lower limb of each of eight healthy men was suspended for 20 days. Biopsy specimens were obtained from the vastus lateralis muscle pre- and post-suspension. RESULTS: The volume of the vastus lateralis muscle was significantly decreased after unloading. The amount of RhoA, RhoGDI or SRF protein in the muscle was not significantly changed post-suspension. An RT-PCR semiquantitative analysis showed increased levels of myostatin mRNA but not Smad2, Smad3 or FLRG mRNA. Unloading did not elicit significant changes in the amount of p-Smad3 or myostatin protein in the muscle. The amount of p-Akt protein was markedly reduced in the unloaded muscle. Lower limb SUSPENSION DID NOT INFLUENCE THE EXPRESSION PATTERN OF FOXO1, FOXO3A OR ATROGIN-1. CONCLUSION: Unloading inducing a mild degree of muscle atrophy may decrease p-Akt and increase myostatin but not SRF-linked mediators.

Effect of intensive interval training during unloading on muscle deoxygenation kinetics.

The present study investigated the effects of intensive interval training during 20-day of unloading on local muscle oxygenation kinetics evaluated by near infrared spectroscopy technique (NIRS). Eleven adult men completed 20-day unloading and were divided into two groups; the control (CON) group and training (TR) group. The TR group engaged in exercise training sessions that consisted of one-legged submaximal cycle exercise using the unloaded leg at 60 approximately 80% of VO(2peak) with intermittent rest periods, 25 min/day every other day. All subjects performed isometric knee extension exercise at 50% of their maximum voluntary contraction force before and after unloading. NIRS Delta[deoxy-Hb/Mb] signal was recorded from m. vastus lateralis and was fitted to an exponential equation in order to determine the kinetics parameters. The time constant (tau) of the % Delta[deoxy-Hb/Mb] was unchanged in the TR group, while it significantly increased in the CON group after unloading (pre, 5.0+/-1.0; post, 7.4+/-1.0 s). It is concluded that 20-day unloading increased the tau, suggesting deterioration of capacity for oxidative phosphorylation and oxygen utilization in a skeletal muscle. Additionally, the preservation of tau in the TR group suggested that intensive interval training could have an impact on the maintenance of muscle oxidative metabolism during unloading.

Effects of 20-day bed rest with and without strength training on postural sway during quiet standing.

AIM: To examine the effect of unweighting as a possible contributory factor to a reduced calf muscle volume on postural sway during quiet standing, changes in postural sway following bed rest with or without strength training were investigated. METHODS: Twelve young men participated in a 20-day bed-rest study. Subjects were divided into a non-training group (BR-Con) and a strength training group (BR-Tr). For the BR-Tr group, training was comprised of dynamic calf-raise and leg-press exercises to maintain the muscle volume of the plantar flexors. Before and after bed rest, subjects maintained quiet standing in a barefoot position on a force platform with their eyes open or closed. During the quiet stance, foot centre-of-pressure (CoP) and the mean velocity of CoP was calculated. Muscle volume of the plantar flexors was computed using axial magnetic resonance images of the leg. RESULTS: After the bed-rest period, the muscle volume decreased in the BR-Con group but not in the BR-Tr group. The mean velocity of CoP as an assessment of postural sway, however, increased in both groups. These results indicate that the strength training during bed rest cannot counteract the increase in postural sway. CONCLUSION: We concluded that postural sway increases following 20 days of bed rest despite maintenance of the muscle volume of plantar flexors as the main working muscles for the human postural standing.

Recruitment of the thigh muscles during sprint cycling by muscle functional magnetic resonance imaging.

The purpose of the present study was to investigate recruitment patterns of the thigh muscles during maximal sprint cycling by muscle functional magnetic resonance imaging (mfMRI). Twelve healthy men participated in this study and performed 2, 5, and 10 sets of 6-s supramaximal cycling with a load of 7.5 % of their body weight with 0.5 min of rest between the sets. Before and immediately after the exercise, T2-weighted MR images, i.e. mfMRI, of the right-thigh were taken to calculate T2 of eleven thigh muscles. Vastus lateralis, semitendinosus, and sartorius were the highest activated, i. e. had the greatest T2 change, among the quadriceps, hamstring, and adductors, respectively, compared with other muscles. Total power output during 2, 5, and 10 sets of sprint cycling was correlated with percent change in T2 in the quadriceps correlated (r (2) = 0.507 to 0.696, p < 0.01), the hamstring (r (2) = 0.162 to 0.335, p < 0.05 approximately 0.001), and the adductor muscles (r (2) = 0.162 to 0.473, p < 0.05 approximately 0.0001). With use of stepwise regression analysis, total power output was significantly correlated with % change in T2 of the vastus medialis (VM) (p < 0.0001) and vastus intermedius (VI) (p < 0.05) (r (2) = 0.698, p < 0.0001). We concluded that eleven thigh muscles were activated non-uniformly, and that the VM and VI play a key role during maximal sprint cycling.

Effects of 20 days of bed rest on the viscoelastic properties of tendon structures in lower limb muscles.

OBJECTIVES: The purpose of this study was to investigate the effects of 20 days' bed rest on the viscoelastic properties of human tendon structures in knee extensor and plantar flexor muscles in vivo. METHODS: Eight healthy men (age: 24+/-4 years, height: 172+/-9 m, body mass: 69+/-13 kg) carried out a 6 degrees head-down bed rest for 20 days. Before and after bed rest, elongation (L) of the tendon and aponeurosis of vastus lateralis (VL) and medial gastrocnemius muscles (MG) during isometric knee extension and plantar flexion, respectively, were determined using real-time ultrasonic apparatus, while the subjects performed ramp isometric contraction up to the voluntary maximum, followed by ramp relaxation. The relationship between estimated muscle force (Fm) and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the Fm-L loop to the area beneath the load portion of the curve. RESULTS: L values above 100 N were significantly greater after bed rest for VL, while there were no significant differences in L values between before and after for MG. The stiffness decreased after bed rest for VL (70.3+/-27.4 v 50.1+/-24.8 N/mm, before and after bed rest, respectively; p = 0.003) and MG (29.4+/-7.5 v 25.6+/-7.8 N/mm, before and after bed rest, respectively; p = 0.054). In addition, hysteresis increased after bed rest for VL (16.5+/-7.1% v 28.2+/-12.9%, before and after bed rest, respectively; p = 0.017), but not for MG (17.4+/-4.4% v 17.7+/-6.1%, before and after bed rest, respectively; p = 0.925). CONCLUSIONS: These results suggested that bed rest decreased the stiffness of human tendon structures and increased their hysteresis, and that these changes were found in knee extensors, but not the plantar flexors.

Effects of equivolume isometric training programs comprising medium or high resistance on muscle size and strength.

Isometric unilateral elbow extension training was conducted for 10 weeks (3 times per week) on 12 young adult men to investigate the effects of equivolume exercise programs with different combinations of intensity and duration on the morphological and functional aspects of the triceps brachii muscle. One group of 6 subjects trained by developing maximal voluntary contraction (MVC) for 6 s per set with 12 sets per session (100%G), while the other group of 6 subjects trained at 60% of MVC for 30 s per set with 4 sets per session (60%G). Training significantly increased the muscle volume ( V(m)), fascicle pennation angle of the triceps brachii, and torque output during concentric and eccentric elbow extensions at three constant velocities of 0.52, 1.57, and 3.14 rad.s(-1) as well as under the training condition, with no significant differences in the relative gains between the two programs. However, 100%G showed significantly greater V(m) than 60%G after training, when V(m) before training was normalized. Thus, only 60%G significantly increased the ratio of torque to V(m) developed in the eccentric actions at the three velocities and concentric action at 1.57 rad.s(-1). The present results indicate that isometric training programs of medium resistance/long duration and high resistance/short duration produce different effects on V(m) and dynamic strength relative to V(m), even if the training volume is equalized between the two protocols.

Inactivity and muscle: effect of resistance training during bed rest on muscle size in the lower limb.

The present study aimed to investigate the effect of dynamic leg press training on the physiological cross-sectional areas (PCSAs) of human lower limb muscles during 20 days of 6 degrees head-down tilt bed rest. Five healthy men comprised the resistance training group (BR-Tr) and data from two previous studies were used to derive a 10-man control group (BR-Cont). The BR-Tr performed two sessions (morning and afternoon session) of dynamic leg press action including knee extension and plantar flexion daily for the bed rest period: (1) three sets of 10 repetitions at 90% of maximum load and (2) 40% of maximum load to exhaustion. The PCSAs of the knee extensor (KE), knee flexor (KF), plantar flexor (PF), and dorsiflexor muscle groups were estimated using serial axial magnetic resonance (MR) images of the right-thigh and leg. After the bed rest period, the BR-Tr showed a significant increase in the PCSA of the KE. Although PCSA of the KF in two groups significantly decreased after bed rest, percentage of change in PCSA of the biceps femoris (long head) and semitendinosus muscles in the BR-Tr, which occupied approximately 70% of the KF, was significantly higher than those in the BR-Cont. Both the BR-Tr and BR-Cont groups showed significant decreases in the PCSA of PF with similar magnitude of 11.6% (P < 0.001) and 11.9% (P < 0.001), respectively. These results suggest that dynamic leg press training during bed rest can prevent deteriorating of the KE and a part of KF, but not the calf muscles.

Changes in muscle size, architecture, and neural activation after 20 days of bed rest with and without resistance exercise.

Nine healthy men carried out head-down bed rest (BR) for 20 days. five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured. Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [-10.9 (SD 6.9)%, P < 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group. The PCSA decreased in NT by -7.8 (SD 0.8)% (P < 0.05) while in TR PCSA showed only an insignificant tendency to decrease [-3.8 (SD 3.8)%]. Changes in force were related more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure.

Muscle function in 164 men and women aged 20--84 yr.

PURPOSE: The purpose of the present study was to investigate the effect of aging in men and women on muscle functional properties, i.e., muscle force and force per unit of cross-sectional area (force/CSA). METHODS: A total of 164 volunteers participated in this study and were divided into five groups according to their chronological age as follows: 20s (20--39 yr old), 40s, 50s, 60s, and 70s (70--84 yr old). Isokinetic (0, 60, 180, and 300 degrees.s(-1)) knee extensor and flexor peak torque, and CSA of the quadriceps femoris (QF) muscle of the mid-thigh were measured. RESULTS: Peak torque during knee extension and flexion was inversely related to age in both men and women. This was the case irrespective of the speed of contraction in both genders (men: r = -0.797 to -0.756, all P < 0.001, women: r = -0.639 to -0.530, all P < 0.001). A significant correlation was observed between CSA of QF and peak torque during isometric knee extension in men (r = 0.827, P < 0.001) and women (r = 0.657, P < 0.001). During isometric contraction, the force/CSA exhibited a significant decrease with increasing age in men (r = -0.518, P < 0.001) but not in women (r = -0.207, NS). CONCLUSION: These results thus suggest that muscle strength losses would be mainly due to a decline in muscle mass in both genders, whereas age-related decline in muscle function in men may also be the result of neural factors, such as muscle recruitment and/or specific tension.

Recruitment plasticity of neuromuscular compartments in exercised tibialis anterior using echo-planar magnetic resonance imaging in humans.

We investigated the recruitment plasticity of the superficial tibialis anterior (TA-s) and deep tibialis anterior (TA-d) regions of neuromuscular compartments (NMCs) in the m. tibialis anterior (TA) during exercise using echo-planar imaging (EPI). Six healthy men performed dorsiflexion exercise at 60% of maximum voluntary contraction at a frequency of 10 contractions/min inside the magnetic resonance imaging. Transaxial EPIs of the right leg were acquired every 6 s at rest (0.5 min), during exercise (2.5 min) and recovery (5 min). In TA-s, significantly higher signal intensities (SIs) were shown than those in TA-d from immediately after starting the exercise to recovery. It has been demonstrated that SI reflects the degree of recruitment in the activated muscle, thus our result suggest that preferential firing of motor neurons in the superficial region of the NMC occurs during exercise in human TA muscle.

Effect of short-duration spaceflight on thigh and leg muscle volume.

PURPOSE: Human skeletal muscle probably atrophies as a result of spaceflight, but few studies have examined this issue. Thus, little is known about the influence of microgravity upon human skeletal muscle, nor is it possible to assess the validity of ground based models of spaceflight. This study tested the hypothesis that the magnitude of spaceflight induced muscle atrophy would be a function of flight duration and greater than that of bed rest. METHODS: Three astronauts flew 9, 15, and 16 d in space. Volume of the knee extensor (quadriceps femoris), knee flexor (hamstrings, sartorius, and gracilis), and plantar flexor (triceps surae) muscle groups was measured using magnetic resonance imaging before and after spaceflight and during recovery. The volume of each muscle group in each image was determined by multiplying cross-sectional area by slice thickness. These values were subsequently summed to calculate muscle volume. RESULTS: Volume changes in the knee extensor, knee flexor, and plantar flexor muscle groups ranged from -15.4 to -5.5, -14.1 to -5.6, and -8.8 to -15.9%, respectively. Muscle volume decreases normalized by flight duration ranged from 0.62 to 1.04% x d(-1). These relative changes appeared to be greater than those that we have reported previously for bed rest (Akima et al., J. Gravitat. Physiol. 4:15-22, 1997). CONCLUSIONS: These results suggest that atrophy as a result of at least 2 wk of spaceflight varied among individuals and muscle groups and that the degree of atrophy appeared to be greater than that induced by 20 d of bed rest.

Leg-press resistance training during 20 days of 6 degrees head-down-tilt bed rest prevents muscle deconditioning.

The purpose of this study was to investigate the effects of resistance training on the morphological and functional properties of human lower limb muscles during 20 days of 6 degrees head-down-tilt bed rest. Nine men were randomly assigned to the resistance training group (BR-Tr, n = 5) or the non-training, control group (BR-Cont, n = 4). Isometric leg-press exercises were performed: 3 s x 30 repetitions (30 s rest between repetitions) daily for 20 days during the bed-rest period. Serial axial magnetic resonance images were taken from the right thigh and leg muscles, and muscle volume, muscle length, and fibre length were estimated. The physiological cross-sectional areas (PCSAs) of the knee extensor, knee flexor, ankle plantarflexor, and ankle dorsiflexor (tibialis anterior) muscle groups were determined as muscle volume multiplied by the cosine of the angle of fibre pennation divided by fibre length. Maximum voluntary contraction (MVC) during knee extension was measured. No significant changes were observed in the PCSA of the knee extensor muscles in BR-Tr group, whereas the PCSA in the BR-Cont group decreased by 7.8%. The PCSA of the knee flexor and plantarflexor muscles in the BR-Tr group and BR-Cont group significantly decreased after bed rest (knee flexors, 10.2% and 11.5%; plantarflexors, 13.0% and 12.8%, respectively). However, in both groups bed rest had no effect on the muscle volume and PCSA of the tibialis anterior. MVC was maintained by resistance training in the BR-Tr group (decreased by 1%). In contrast, a decline of strength was observed in the BR-Cont group (-16%), but this result was not statistically significant. These results suggest that isometric leg-press training prevents the deconditioning (i.e. atrophy and decline of strength) of the knee extensor muscle group.

In vivo moment arm determination using B-mode ultrasonography.

The tendon excursion of the tibialis anterior (TA) muscle was measured in vivo using B-mode ultrasonography in seven subjects under three force levels (0, 30 and 60% maximal voluntary contraction, MVC). For each force level, the TA moment arm (m) was determined by calculating the derivative of the tendon excursion relative to the ankle angle (a). A dynamometer controlled the ankle angle while force levels were monitored. The parametric model proposed by Miller and Dennis (1996), m = R sin(a + delta), where R is the largest moment arm and delta represents the offset angle of R from 90 degrees, was used in a least-squares fit of the relationship between moment arm and ankle angle. The R values at 0% MVC were significantly smaller than those at 30 and 60% MVC. The values of calculated moment arm at 0% MVC were not considered adequate estimates of the TA moment arm because of the possible confounding effect of the slackness of the relaxed muscle-tendon unit in more dorsiflexed positions. The moment arm values at 30 and 60% MVC were believed to provide reliable estimates of those of TA since the application of tension probably reduced the effects of the slackness of the muscle-tendon unit and tendon elongation on tendon excursion measurement at these force levels. Since the ultrasonographic technique is an in vivo application of the tendon excursion technique and therefore takes the functional meaning into consideration, it can yield more significant moment arms than other in vivo or cadaver techniques.

Changes in the elastic properties of tendon structures following 20 days bed-rest in humans.

The purpose of this study was to investigate the effects of 20 days bed-rest on the elastic properties of tendon structures of the human knee extensor muscles in vivo. Six healthy men carried out a 6 degrees head-down bed-rest for 20 days. Muscle volume and maximal voluntary contraction (MVC) torque of the quadriceps femoris muscle significantly decreased by an average of 7.8 (SD 2.7)% and 14.9 (SD 6.9)%, respectively. Before and after bed-rest, the elongation (l) of the tendon and aponeurosis of vastus lateralis muscle was measured directly by ultrasonography, while the subjects performed ramp isometric knee extension up to MVC. The extent of l tended to be greater after bed-rest. The l above 110 N was significantly greater after bed-rest. Furthermore, the mean stiffness after bed-rest [35.5 (SD 7.8) N x mm(-1)] was significantly lower than that before bed-rest [52.6 (SD 19.2) N x mm(-1)]. The rate of torque development significantly reduced after bed-rest by an average of 47%, and the bed-rest induced a lengthening in the electromechanical delay (mean 21%). These results suggest that bed-rest results in a decrease in the stiffness of tendon structures with a reduction of muscle strength and volume. These adaptations of the tendon structures to bed-rest would bring about the changes in electromechanical delay and rate of torque development.

The use of magnetic resonance images to investigate the influence of recruitment on the relationship between torque and cross-sectional area in human muscle.

The purpose of the present study was to investigate the effect of recruitment on the relationship between peak torque and physiological cross-sectional area (PCSA) in human muscle. A group of 11 healthy men participated in this study. Isokinetic knee extension torques at seven (0, 30, 60, 120, 180, 240, and 300 degrees x s(-1)) velocities were determined. Magnetic resonance imaging (MRI) was performed to calculate PCSA of right quadriceps femoris (QF) muscle. Exercise-induced contrast shifts in spin-spin relaxation time (T2)-weighted MRI were taken at rest and immediately after repetitive knee-extension exercise and T2 of QF were calculated. The MRI pixels with T2 values more than 1 SD greater than the means at rest were considered to represent QF muscle that had contracted. The area of activated PCSA within the total in QF was expressed as percentage activated PCSA and used as an index of muscle recruitment. The PCSA correlated with peak torque at 0 degree x s(-1) (r = 0.615, P<0.05); in contrast, activated PCSA correlated with peak torque at 120 degrees x s(-1) (r = 0.603, P<0.05) and 180 degrees x s(-1) (r = 0.606, P<0.05). Additionally, there was a significant difference in correlation coefficients between the activated PCSA-peak torque relationship and the PCSA-torque relationship (P<0.05). These results suggested that muscle recruitment affects the PCSA-torque relationship.

Early phase adaptations of muscle use and strength to isokinetic training.

The purpose of this study was to investigate the effect of short periods of isokinetic resistance training on muscle use and strength. Seven men trained the right quadriceps femoris muscles (QF) 9 d for 2 wk using 10 sets of 5 knee extensions each day. Isometric and isokinetic torques of QF were measured at six angular velocities. Cross-sectional areas (CSA) of QF were determined from axial images using magnetic resonance imaging (MRI). Transverse relaxation time (T2) and activated area of QF, which represented the area greater than the mean resting T2 + ISD in MR[pixels, were calculated at rest and immediately after repetitive isokinetic knee extensions based on T2-weighted MR images. Muscle fiber types, fiber area, and phosphofructokinase (PFK) activities were determined from biopsies of the vastus lateralis muscle. No changes were found in CSA of QF, muscle fiber types, fiber area, and PFK activities after the training. Isometric and isokinetic peak torques at 60-240 degrees x s(-1) and relative area of QF activated by knee extensions increased significantly after the training. These results suggest that muscle strength increases after short periods of isokinetic resistance training without muscle hypertrophy would be due to increased muscle contractile activity.