Effect of aging on human muscle architecture

The effect of aging on human gastrocnemius medialis (GM) muscle architecture was evaluated by comparing morphometric measurements on 14 young (aged 27-42 yr) and on 16 older (aged 70-81 yr) physically active men, matched for height, body mass, and physical activity. GM muscle anatomic cross-sectional area (ACSA) and volume (Vol) were measured by computerized tomography, and GM fascicle length (Lf) and pennation angle (theta) were assessed by ultrasonography. GM physiological cross-sectional area (PCSA) was calculated as the ratio of Vol/Lf. In the elderly, ACSA and Vol were, respectively, 19.1% (P < 0.005) and 25.4% (P < 0.001) smaller than in the young adults. Also, Lf and were found to be smaller in the elderly group by 10.2% (P < 0.01) and 13.2% (P < 0.01), respectively. When the data for the young and elderly adults were pooled together, significantly correlated with ACSA (P < 0.05). Because of the reduced Vol and Lf in the elderly group, the resulting PCSA was found to be 15.2% (P < 0.05) smaller. In conclusion, this study demonstrates that aging significantly affects human skeletal muscle architecture. These structural alterations are expected to have implications for muscle function in old age.

Effect of resistance training on skeletal muscle-specific force in elderly humans

This study assessed muscle-specific force in vivo following strength training in old age. Subjects were assigned to training (n = 9, age 74.3 +/- 3.5 yr; mean +/- SD) and control (n = 9, age 67.1 +/- 2 yr) groups. Leg-extension and leg-press exercises (2 sets of 10 repetitions at 80% of the 5 repetition maximum) were performed three times/wk for 14 wk. Vastus lateralis (VL) muscle fascicle force was calculated from maximal isometric voluntary knee extensor torque with superimposed stimuli, accounting for the patella tendon moment arm length, ultrasound-based measurements of muscle architecture, and antagonist cocontraction estimated from electromyographic activity. Physiological cross-sectional area (PCSA) was calculated from the ratio of muscle volume to fascicle length. Specific force was calculated by dividing fascicle force by PCSA. Fascicle force increased by 11%, from 847.9 +/- 365.3 N before to 939.3 +/- 347.8 N after training (P < 0.05). Due to a relatively greater increase in fascicle length (11%) than muscle volume (6%), PCSA remained unchanged (pretraining: 30.4 +/- 8.9 cm(2); posttraining: 29.1 +/- 8.4 cm(2); P > 0.05). Activation capacity and VL muscle root mean square electromyographic activity increased by 5 and 40%, respectively, after training (P < 0.05), indicating increased agonist neural drive, whereas antagonist cocontraction remained unchanged (P > 0.05). The VL muscle-specific force increased by 19%, from 27 +/- 6.3 N/cm(2) before to 32.1 +/- 7.4 N/cm(2) after training (P < 0.01), highlighting the effectiveness of strength training for increasing the intrinsic force-producing capacity of skeletal muscle in old age.

Effect of strength training on human patella tendon mechanical properties of older individuals

This study investigated the effect of strength training on the mechanical properties of the human patella tendon of older individuals. Subjects were assigned to training (n = 9; age 74.3 +/- 3.5 years, body mass 69.7 +/- 14.8 kg and height 163.4 +/- 9.1 cm, mean +/- S.D.) and control (n = 9; age 67.1 +/- 2 years, body mass 73.5 +/- 14.9 kg and height 168.3 +/- 11.5 cm) groups. Strength training (two series of 10 repetitions at 80 % of five-repetition maximum) was performed three times per week for 14 weeks using leg extension and leg press exercises. Measurements of tendon elongation during a ramp isometric knee extension were performed before and after training and control periods in vivo using ultrasonography. Training caused a decreased tendon elongation and strain at all levels of force and stress (P < 0.01). Baseline tendon elongation and strain at maximal tendon load were 4.7 +/- 1.1 mm and 9.9 +/- 2.2 %, respectively (maximum force: 3346 +/- 1168 N; maximum stress: 40 +/- 11 MPa). After training, these values decreased to 2.9 +/- 1.2 mm and 5.9 +/- 2.4 % (P < 0.01), respectively (maximum force: 3555 +/- 1257 N; maximum stress: 42 +/- 11 MPa). Tendon stiffness increased by 65 % (2187 +/- 713 to 3609 +/- 1220 N mm-1; P < 0.05) and Young's modulus increased by 69 % (1.3 +/- 0.3 to 2.2 +/- 0.8 GPa; P < 0.01). As a result of these changes, the rate of torque development increased by 27 % (482.8 +/- 302.5 to 612.6 +/- 401 N m s-1; P < 0.01) following training. No significant changes occurred in any measured variables in the control group (P > 0.05). This study shows for the first time that strength training in old age increases the stiffness and Young's modulus of human tendons. This may reduce the risk of tendon injury in old age and has implications for contractile force production and the rapid execution of motor tasks.

Effect of ageing on the electrical and mechanical properties of human soleus motor units activated by the H reflex and M wave

This study was designed to investigate the effect of ageing on the mechanical and electromyographic (EMG) characteristics of the soleus motor units (MUs) activated by the maximal Hoffmann reflex (Hmax) and by the direct muscle compound action potential (Mmax). Eleven young (mean age 25 +/- 4 years) and ten elderly (mean age 73 +/- 5 years) males took part in this investigation. The senior group presented lower amplitudes of Mmax (-57 %, P < 0.001) and Hmax (-68 %, P < 0.001) waves compared to the younger population. These were associated with a depression of relative twitch torque of the plantar flexors. The average values of the Hmax/Mmax ratio did not statistically differ between the two populations, despite a tendency for lower values (~23 %) in the senior group. However, the older adults showed a greater relative amplitude of the sub-maximal M wave evoked at Hmax (MatHmax) than did the younger males (young 5 % vs. elderly 29 % of the Mmax, P < 0.01). This finding suggests an increased homogeneity between the excitability threshold of sensory and motor axons. The twitch torque at Hmax (PtH-M) was subsequently calculated by subtraction from the total twitch torque of the mechanical contamination associated with MatHmax. The resulting PtH-M was significantly lower in the elderly (-59 %, P < 0.001). Despite a discrepancy of 20 % between the two groups, the mechanical ratio (PtH-M/PtM; PtM, twitch tension related to the Mmax compound action potential), like the EMG ratio, did not statistically differ between the young and older individuals. Nevertheless, the senior subjects exhibited a higher twitch/EMG ratio for the reflexively activated MUs (PtH-M/Hmax) than the younger individuals (+40 %, P < 0.05). This finding suggests an on-going neuromuscular remodelling, resulting in an increased innervation ratio. The neural rearrangement may be viewed as a compensatory adaptation of the motor system to preserve the mechanical efficiency of the surviving MUs, despite the age-related impairment of the segmental reflex system. This phenomenon is confirmed by the maintenance, with senescence, of the approximately constant values of the twitch/EMG ratio for the entire motor pool (PtM/Mmax).

Effects of short-term, integrated body mass reduction program on maximal oxygen consumption and anaerobic alactic performance in obese subjects

The study investigated the effect of a short-term (3-week) body mass reduction program, combining energy-restricted diet, nutritional education, psychological counselling and aerobic exercise training (DEP-AT) on maximal oxygen consumption (VO2max) and anaerobic alactic performance evaluated with different techniques in obese patients (grade II and III). Fifty-three (14 males, 39 females) obese subjects [average +/- SD body mass index (BMI): 41.6 +/- 4.2 kg/m2] were tested before and after the DEP-AT program characterised by a daily conditioning protocol of aerobic exercise on cycloergometer, treadmill and armergometer for a total duration of 35 min at an intensity corresponding to 50% of individual VO2max during the first week of the program and at 60% in the following 2 weeks. VO2max was determined with the cycloergometric indirect method. Short-term alactic anaerobic performance was evaluated with: a) jumping test (5 consecutive jumps with maximal effort, Bosco technique), b) short sprint running test (8m), and c) stair climbing test (modified Margaria test). The DEP-AT program induced a significant weight loss (-4.57 +/- 1.26%, p < 0.001) and a significant VO2max increase (14.1 +/- 20.5%, p < 0.001). After the DEP-AT program, lower limb alactic anaerobic power output, calculated on a per kg body mass basis, increased significantly both in jumping and in stair climbing (20.1 +/- 24.8%, p < 0.001 and 13.5 +/- 19.75%, p < 0.001, respectively), as well as average horizontal velocity during short sprinting (7.2 +/- 17.6%, p < 0.01). Power output was a major determinant of the motor performance, being significantly correlated with: a) vertical displacement of the centre of gravity (R2 = 0.884, p < 0.001) in jumping test, b) vertical velocity (R2 = 0.348, p < 0.001) in stair climbing test, and c) horizontal velocity (R2 = 0.394, p < 0.001) in short running test. In conclusion, short-term DEP-AT program induces significant improvements in both aerobic capabilities and anaerobic performance, possibly through the combination of a number of contributory mechanisms, such as exercise-mediated training, shift in the balance between parasympathetic and sympathetic activity, a weight-loss dependent shift toward a more favourable region of the muscle power-velocity curve, acquisition of a certain degree of motor skill during the conditioning program, improvement of self-esteem and motivation.

Strength and power changes of the human plantar flexors and knee extensors in response to resistance training in old age

AIM

The aim of the present study was to assess and compare the improvements of muscle strength and power induced by a 16-week resistive programme in a population of 16 older men aged 65-81 years.

METHODS

Training was performed three times per week at an intensity of 80% of one repetition maximum (1RM) and consisted of both calf raise and leg press exercises. Before-, during- and after-training, maximum isometric and isokinetic torques, maximum power, 1RM, muscle cross-sectional area (CSA) and electromyographic activity (EMG) of the plantar flexors (PF) and knee extensors (KE) were examined.

RESULTS

For the KE and PF, respectively, training resulted in a 29.9 +/- 4.4% (mean +/- SE) and 21.6 +/- 5.4% increase in 1RM (P < 0.001-0.01), a 19.4 +/- 4.3 and 12.4 +/- 4.7% (P < 0.001-0.05) increase in maximum isometric torque, and a 24.1 +/- 6.3 and 33.1 +/- 10.9% (P < 0.05) increase in maximum muscle power, calculated from torque-angular velocity curves. The large increase in torque and power was partly accounted by a significant increase in the CSA of the PF (5.0 +/- 0.7%) and KE (7.4 +/- 0.7%), while no significant changes in integrated EMG activity of vastus lateralis and soleus muscles, and in extrapolated maximum shortening velocity were found. After training, a significant increase in torque/CSA (10.3 +/- 4%, P < 0.05) was found for the KE but not for the PF.

CONCLUSION

Hence, hypertrophy cannot alone justify the increase in torque, and other factors, such as an increase in individual fibre-specific tension (in the case of KE), a decrease in antagonist muscles' coactivation, an improved co-ordination and an increased neural drive of the other heads of quadriceps may have contributed to the increments in strength. The significant increase in muscle power seems particularly noteworthy with respect to daily activities involving the displacement of the body over time, namely, the generation of muscle power.

Influence of simulated microgravity on human skeletal muscle architecture and function

Ten male volunteers underwent a period of prolonged bed rest. Four subjects performed exercise countermeasures 2-3 times per week, while 6 subjects received no countermeasures. After bed rest plantarflexor force declined significantly (P < 0.001) in both exercise (-42%) and control (-55%) groups. The internal architecture of the gastrocnemius medialis (GM) muscle was significantly altered. This was associated with a reduction in fascicle shortening during isometric contraction. Exercise countermeasures partially mitigated the loss of muscle force and function following 90 days of bed rest.

Plantar flexor activation capacity and H reflex in older adults: adaptations to strength training

The purpose of this study was to investigate whether the voluntary neural drive and the excitability of the reflex arc could be modulated by training, even in old age. To this aim, the effects of a 16-wk strengthening program on plantar flexor voluntary activation (VA) and on the maximum Hoffman reflex (H(max))-to-maximum M wave (M(max)) ratio were investigated in 14 elderly men (65-80 yr). After training, isometric maximum voluntary contraction (MVC) increased by 18% (P < 0.05) and weight-lifting ability by 24% (P < 0.001). Twitch contraction time decreased by 8% (P < 0.01), but no changes in half relaxation time and in peak twitch torque were observed. The VA, assessed by twitch interpolation, increased from 95 to 98% (P < 0.05). Pretraining VA, also evaluated from the expected MVC for total twitch occlusion, was 7% higher (P < 0.01) than MVC. This discrepancy persisted after training. The interpolated twitch torque-voluntary torque relationship was fitted by a nonlinear model and was found to deviate from linearity for torque levels >65% MVC. Compared with younger men (24-35 yr), the H(max)- to M(max) ratio and nerve conduction velocity (H index) of the older group were significantly lower (42%, P < 0.05; and 29%, P < 0.001, respectively) and were not modulated by training. In conclusion, older men seem to preserve a high VA of plantar flexors. However, the impaired functionality of the reflex pathway with aging and the lack of modulation with exercise suggest that the decrease in the H(max)- to M(max) ratio and H index may be related to degenerative phenomena.

Effects of a 16-week progressive high-intensity strength training (HIST) on indexes of bone turnover in men over 65 years: a randomized controlled study

The aim of the present study was to evaluate the effects of a 16-week progressive high-intensity strength training (HIST) program on peripheral markers of bone turnover (bone Gla protein, BGP; bone alkaline phosphatase, B-AP; N-terminal propeptide of type I procollagen, PINP; C-terminal cross-linked telopeptide of type I collagen, ICTP) in healthy, elderly men over 65 yr of age. Thirty healthy men (aged 65-81 yr), performing light to moderate daily physical activity, were randomly divided into two groups. Group 1 (no.=16) followed a supervised 16-week progressive HIST program, while subjects of group 2 (no.=14), used as controls, were requested to maintain their habitual level of physical activity for 16 weeks. HIST program consisted of 6 different sets of exercise (2 involving the major muscle groups of the lower limb and 4 involving those of the upper limb). Three sessions/ week, during which 10 repetitions of each exercise set were completed, were performed. Lower limb exercises shifted from 50 to 80% of the one maximal repetition (1 MR) during the first month of the protocol and were thereafter maintained at an intensity of 80% 1 MR throughout the training. Upper limb exercises shifted from 40 to 65% of 1 MR with a similar pattern. All sessions were preceded by 15 min of cycloergometer exercise at 50% of maximal oxygen uptake and by a warm-up of 15 repetitions at 20% of 1 MR of each exercise set. The HIST program did not significantly change BGP (mean SE, before: 15.6 +/- 1.2 microg/l vs after: 16.0 +/- 1.2 microg/l, NS) and PINP levels (before: 44.6 +/- 6.7 microg/l vs after: 43.1 +/- 6.0 microg/l, NS). On the contrary, serum B-AP significantly increased (before: 50.2 +/- 6.1 IU/l vs after: 62.3 +/- 7.0 lU/l, p<0.001) and serum ICTP slightly reduced (before: 4.0 +/- 0.3 microg/l vs after: 3.8 +/- 0.3 microg/l, p<0.05). When bone turnover was expressed as the ratio between bone formation to bone resorption (B-AP/ICTP ratio), a significant improvement in this ratio was found in all subjects of group 1 (before: 12.9 +/- 1.3 lU/microg vs after: 17.3 +/- 1.5 IU/microg, p<0.0001), while no significant changes were observed in Group 2. No significant changes of IGF-I levels were observed after the HIST program (before: 94.9 +/- 9.4 microg/l vs after: 89.9 +/- 9.7 microg/l). No significant changes of BGP, PINP, B-AP, ICTP, B-AP-ICTP ratio and IGF-I levels were observed in controls (group 2) during the 16 weeks of observation. Although the positive effects of a progressive HIST program on B-AP levels and B-AP-ICTP ratio seem promising, the support of bone mass measurement and the determination of other bone markers are requested to better identify exercise protocol (duration, intensity) for elderly people.

Changes in motor control and muscle performance after a short-term body mass reduction program in obese subjects

Two hundred and thirty obese subjects (age: 18-77 yr, BMI: 31.1-65.8 kg/m2) were studied before and after a 3-week body mass reduction (BMR) program, coupling restricted energy diet (1200-1500 kcal/day) with low intensity exercise prescription. It involved 5 days per week (consisting of one-hour dynamic aerobic standing and floor exercise plus 30 min of cycloergometer exercise at 60 W or, alternatively, 4 km outdoor leisure walking on flat terrain) and psychological counseling. One-leg standing balance test (OLSB) and stair climbing test (SCT) were employed to assess motor control and maximal lower limb muscle power, respectively. The BMR program induced a significant weight loss (4.1%; p<0.001), a higher reduction of body mass index (BMI) being observed in males than in females (p<0.001). OLSB performance time increased by 20.5% (p<0.001) after treatment, the improvement being evident in both genders. A 20.8% reduction in SCT time (p<0.05) was also observed and corresponded to a 13.2% increase (p<0.001) in average absolute muscle power and 15.0% increase (p<0.001) in specific muscle power (i.e. the power output per kg of body mass), with no differences between genders. In conclusion, in spite of the moderate reduction of body mass after restricted energy diet and low intensity physical conditioning, significant improvements in motor control and performance, likely to ameliorate the execution of simple daily activities, were observed in obese subjects.

Maximal instantaneous muscular power after prolonged bed rest in humans

A reduction in lower limb cross-sectional area (CSA) occurs after bed rest (BR). This should lead to an equivalent reduction in maximal instantaneous muscular power (W(p)) if the body segments' lengths remain unchanged. W(p) was determined during maximal jumps off both feet on a force platform before and on days 2, 6, 10, 32, and 48 after a 42-day duration BR. CSA of thigh muscles was measured by magnetic resonance imaging before and on day 5 after BR. Before BR, W(p) was 3.63 +/- 0.43 kW or 48.6 +/- 3.3 W/kg. On days 2 and 6 after BR, W(p) was reduced by 23.7 +/- 6.9 and 22.7 +/- 5.4% (P < 0.01), respectively. Thigh extensors CSA (CSAEXT) was 16.7 +/- 4.7% (P < 0.01) lower than before. When normalized per CSAEXT, W(p) was reduced by only 4.8 +/- 4.5% (P < 0.05). By day 48 of recovery, W(p) had returned to baseline values. Therefore, if W(p) is appropriately normalized for CSA of the extensor muscles, the reduction in CSAEXT explains most of the decrease in W(p) decrease after BR. Other factors such as a deficit in neural activation or a decrease in fiber-specific tension may account for only 5% of the W(p) loss after BR.

Aerobic and anaerobic performance before and after a short-term body mass reduction program in obese subjects

The cardiovascular response to an aerobic cycloergometer exercise test (ACET, 15 min at 60 W, 60 rpm) and the maximally attainable muscle power output, assessed by a stair climbing test (SCT), were evaluated in 60 obese patients (41 females and 19 males; age: 18-68 yr; body mass index, BMI: 40.8+/-4.8 kg/m2) before and after a 3-week body mass reduction (BMR) program, entailing integrated energy-restricted diet (1200-1500 kcal/day), low-grade aerobic exercise conditioning and individual and/or group psychological therapy. The daily conditioning protocol (5 days/week) consisted of: 1) 30 min of indoor jogging and dynamic aerobic standing and floor exercises performed with arms and legs, under the guidance of a therapist; 2) 30 min of cycloergometer exercise at 60 W; and/or 3) 4-km outdoor leisure walking on flat terrain. Three weeks of BMR program induced a significant weight loss (-4.5 %; p<0.001), a reduction of systolic (-11+/-14 mmHg, -7.3%,p<0.001) and diastolic (-7+/-9 mmHg, -7.3%,p<0.001) resting arterial blood pressure, as well as a reduction of heart rate at rest (-18.6%,p<0.001), during ACET (-11.3%,p<0.001) and 5 min thereafter (-14.8%,p<0.001). The subjective rating of perceived exertion in terms of breathlessness and general fatigue during ACET, scored on a 0-100 visual analogic scale, was significantly reduced (p<0.001) after BMR program. A 11.2% decrease in SCT time (p<0.001) was also observed, corresponding to a 9.6% increase (p<0.001) in average muscle power (W) and 14.6% increase (p<0.001) in specific muscle power (W.kg(-1)). In conclusion, a combination of energy restricted diet, low intensity aerobic exercise and psychological counselling appears to significantly improve both aerobic and anaerobic performance in morbidly obese subjects. Different factors (ie, reduction of body mass, shift in the balance between parasympathetic and sympathetic activity, a weight-loss dependent shift toward a more favourable region of the muscle power-velocity curve, acquisition of a certain degree of motor skillfulness during the conditioning program, improvement of self-esteem and motivation) might be responsible, alone or in combination, for these short-term positive effects of BMR program.

The interplay of central and peripheral factors in limiting maximal O2 consumption in man after prolonged bed rest

1. The effects of bed rest on the cardiovascular and muscular parameters which affect maximal O2 consumption (VO2,max) were studied. The fractional limitation of VO2,max imposed by these parameters after bed rest was analysed. 2. The VO2,max, by standard procedure, and the maximal cardiac output (Qmax), by the pulse contour method, were measured during graded cyclo-ergometric exercise on seven subjects before and after a 42-day head-down tilt bed rest. Blood haemoglobin concentration ([Hb]) and arterialized blood gas analysis were determined at the highest work load. 3. Muscle fibre types, oxidative enzyme activities, and capillary and mitochondrial densities were measured on biopsy samples from the vastus lateralis muscle before and at the end of bed rest. The measure of muscle cross-sectional area (CSA) by NMR imaging at the level of biopsy site allowed computation of muscle oxidative capacity and capillary length. 4. The VO2,max was reduced after bed rest (-16.6%). The concomitant decreases in Qmax (-30.8%), essentially due to a change in stroke volume, and in [Hb] led to a huge decrease in O2 delivery (-39.7%). 5. Fibre type distribution was unaffected by bed rest. The decrease in fibre area corresponded to the significant reduction in muscle CSA (-17%). The volume density of mitochondria was reduced after bed rest (-16.6%), as were the oxidative enzyme activities (-11%). The total mitochondrial volume was reduced by 28.5%. Capillary density was unchanged. Total capillary length was 22.2% lower after bed rest, due to muscle atrophy. 6. The interaction between these muscular and cardiovascular changes led to a smaller reduction in VO2,max than in cardiovascular O2 transport. Yet the latter appears to play the greatest role in limiting VO2,max after bed rest (> 70% of overall limitation), the remaining fraction being shared between peripheral O2 diffusion and utilization.

In vivo human gastrocnemius architecture with changing joint angle at rest and during graded isometric contraction

1. Human gastrocnemius medialis architecture was analysed in vivo, by ultrasonography, as a function of joint angle at rest and during voluntary isometric contractions up to the maximum force (MCV). maximum force (MVC). 2. At rest, as ankle joint angle increased from 90 to 150 deg, pennation increased from 15.8 to 27.7 deg, fibre length decreased from 57.0 to 34.0 mm and the physiological cross-sectional area (PCSA) increased from 42.1 to 63.5 cm2. 3. From rest to MVC, at a fixed ankle joint angle of 110 deg, pennation angle increased from 15.5 to 33.6 deg and fibre length decreased from 50.8 to 32.9 mm, with no significant change in the distance between the aponeuroses. As a result of these changes the PCSA increased by 34.8%. 4. Measurements of pennation angle, fibre length and distance between the aponeuroses of the gastrocnemius medialis were also performed by ultrasound on a cadaver leg and found to be in good agreement with direct anatomical measurements. 5. It is concluded that human gastrocnemius medialis architecture is significantly affected both by changes of joint angle at rest and by isometric contraction intensity. The remarkable shortening observed during isometric contraction suggests that, at rest, the gastrocnemius muscle and tendon are considerably slack. The extrapolation of muscle architectural data obtained from cadavers to in vivo conditions should be made only for matching muscle lengths.

Human quadriceps cross-sectional area, torque and neural activation during 6 months strength training

Quadriceps muscle and fibre cross-sectional areas (CSA), torque and neural activation were studied in seven healthy males during 6 months of weight training on alternate days with six series of eight unilateral leg extensions at 80% of one repetition maximum. After training, the quadriceps cross-sectional area increased by 18.8 +/- 7.2% (P < 0.001) and 19.3 +/- 6.7% (P < 0.001) in the distal and proximal regions respectively, and by 13.0 +/- 7.2% (P < 0.001) in the central region of the muscle. Hypertrophy was significantly different between and within the four constituents of the quadriceps. Biopsies of the vastus lateralis at mid-thigh did not show any increase in mean fibre cross-sectional area. Maximum isometric voluntary torque increased by 29.6 +/- 7.9%-21.1 +/- 8.6% (P < 0.01-0.05) between 100 degrees and 160 degrees of knee extension, but no change in the optimum angle (110 degrees-120 degrees) for torque generation was found. A 12.0 +/- 10.8% (P < 0.02) increase in torque per unit area together with a right shift in the IEMG-torque relation and no change in maximum IEMG were observed. Time to peak isometric torque decreased by 45.8% (P < 0.03) but no change in time to maximum IEMG was observed. In conclusion, strength training of the quadriceps results in a variable hypertrophy of its components without affecting its angle-torque relation. The increase in torque per unit area, in the absence of changes in IEMG, may indicate changes in muscle architecture. An increase in muscle-tendon stiffness may account for the decrease in time to peak torque.

Hypertrophic response of human skeletal muscle to strength training in hypoxia and normoxia

The purpose of this study was to test the hypothesis that work-induced skeletal muscle hypertrophy may be reduced by training in chronic hypobaric hypoxia compared to normoxia. Five healthy males [mean age 34.4 (SEM 2.2) years] performed strength training of the elbow flexors for 1 month, at altitude (A) (5050 m) and with the same absolute loads at sea level (SL), 8 months later. The EF cross-sectional area (CSA), determined at mid-arm by nuclear magnetic resonance imaging, increased by 11.3 (SEM 3.7)% (P < 0.05) at A and 17.7 (SEM 4.5)% (P < 0.05) at SL. Isometric maximal voluntary contraction (MVC) increased by 9.5 (SEM 2.6)% (P < 0.05) at A and 13.6 (SEM 2.4)% (P < 0.05) at SL. The CSA and MVC changes in A were significantly smaller than at SL (P < 0.05). Muscle specific tension did not change in either condition. No changes in muscle plus bone or MVC of the untrained, controlateral arm were observed. Thus, although there was no indication of muscle wasting at A, the hypertrophic response of skeletal muscle when trained in chronic hypoxia seemed to be significantly lower than that produced in normoxia. This effect could have arisen either from a direct depression of protein synthesis and/or hormonal changes provoked by hypoxia.

Isokinetic torques and kicking maximal ball velocity in young soccer players

The purpose of this study is to assess if there is any correlation between isokinetic testing and field performance of young soccer players. The isokinetic peak torques of the knee extensor muscles in sitting position (TKE), and those of the hip flexor muscles in standing position (THF) were measured in 24 junior soccer players. Four angular velocities (omega = 1.05, 3.14, 4.19, 5.23 rad.s-1 or 60, 180, 240, 300 deg.s-1) were used for the knee extensors and three (1.05, 3.14, 4.19 rad.s-1) for the hip flexors. On the field the subjects were asked to kick a stationary soccer ball as fast as possible against a barrier and the mean linear velocity over a 10 m path (v) was measured. TKE of the non dominant limb were higher than those of the opposite one at the three highest omega (p < 0.05). On the contrary the THF of the dominant limbs were higher than those of the controlateral, at the two highest omega. When the ball was kicked by the dominant or non dominant limbs, the mean values and standard deviations (+/- SD) of v were 23.6 (+/- 2.5) and 21.4 (+/- 2.6) m.s-1. Torques and v were always positively correlated to each other; however, only in few cases was this relationship statistically significant. In conclusion the isokinetic torques do not seem to be good predictors of v, one of the several factors which determine the global performances of the soccer players.

Growth hormone (GH) treatment in GH-deficient adults: effects on muscle size, strength and neural activation

The effects of 6 months of recombinant growth hormone (GH) treatment (0.5 IU kg-1 per week) on muscle size, strength and neural activation (EMG) was studied in eight adults with childhood onset GH deficiency (GHD). Before treatment, height, body mass (BM) and lean body mass (LBM) of the GHD subjects were significantly lower (P < 0.01) from those recorded in eight healthy controls, while no significant differences were found between the body mass index (BMI) of the two populations. Thigh muscle + bone cross-sectional area (CSAM+B) and lower limb muscle plus bone volume (LLVM+B) of the GHD patients were 66.1 +/- 13.7% and 47.6 +/- 6.8% of those recorded in the controls (P < 0.01), whereas no difference in CSA/height2 was found between the two groups. By contrast, LLVM+B/height3 was 82.0 +/- 19.0% that of the controls (P < 0.05). Similarly, quadriceps muscle strength (MVC) of the GHD patients was 63.2 +/- 12.4% that of controls (P < 0.01), while no significant differences in the force per unit area (F/CSA) and per body mass (F/BM) were found. After 6 months of GH treatment LBM increased by 6.0 +/- 4.2% (P < 0.02), CSAM+B by 14.5 +/- 12.7% (P < 0.01) and LLVM+B by 10.1 +/- 7.3% (P < 0.01), absolute differences from the normals still persisting. However, the LLVM+B/height3 of the GHD patients after treatment was no longer significantly different from that of the controls. Quadriceps MVC increased by 9.8 +/- 12.0% (P < 0.02), differences from the controls being still significant, whereas the F/CSA and F/BM did not change. A right shift of the integrated EMG/Force relation, with no change in the maximal integrated EMG (iEMG) activity, was observed in the patients after treatment. In conclusion, the current study shows that adults with childhood onset GHD have a reduced skeletal muscle mass and strength which seem to be positively influenced by 6 months of GH treatment.

Determinants of peak muscle power: effects of age and physical conditioning

The relationships between absolute peak muscle power (Wpeak), muscle cross sectional area (CSAtot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5'-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20-35 years; B, 9 S aged 35-50 years; C, 9 S aged more than 50 years; D, 13 children aged 8-13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The Wpeak was measured during a maximal vertical high jump off both feet on a force platform. The CSAtot was measured anthropometrically. The [ATP] and [PC] were determined by 31Phosphorus nuclear magnetic resonance spectroscopy. The Wpeak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSAtot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in Wpeak were only partially accounted for by changes in CSAtot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of Wpeak with increasing age and training. An important role may be played by hormonal, particularly at puberty, and neural factors.

Assessment of human knee extensor muscles stress from in vivo physiological cross-sectional area and strength measurements

The physiological cross-sectional areas (CSAp) of the vastus lateralis (VL), vastus intermedius (VI), vastus medialis (VM) and rectus femoris (RF) were obtained, in vivo, from the reconstructed muscle volumes, angles of pennation and distance between tendons of six healthy male volunteers by nuclear magnetic resonance imaging (MRI). In all subjects, the isometric maximum voluntary contraction strength (MVC) was measured at the optimum angle at which peak force occurred. The MVC developed at the ankle was 746.0 (SD 141.8) N and its tendon component (Ft), given by a mechanical advantage of 0.117 (SD 0.010), was 6.367 (SD 1.113) kN. To calculate the force acting along the fibres (Ff) of each muscle, Ft was divided by the cosine of the angle of pennation and multiplied for (CSAp.sigma CSAp-1), where sigma CSAp was the sum of CSAp of the four muscles. The resulting Ff values of VL, VI, VM and RF were: 1.452 (SD 0.531) kN, 1.997 (SD 0.187) kN, 1.914 (SD 0.827) kN, and 1.601 (SD 0.306) kN, respectively. The stress of each muscle was obtained by dividing these forces for the respective CSAp which was: 6.24 x 10(-3) (SD 2.54 x 10(-3)) m2 for VL, 8.35 x 10(-3) (SD 1.17 x 10(-3)) m2 for VI, 6.80 x 10(-3) (SD 2.66 x 10(-3)) m2 for VM and 6.62 x 10(-3) (SD 1.21 x 10(-3)) m2 for RF. The mean value of stress of VL, VI, VM and RF was 250 (SD 19) kN m-2; this value is in good agreement with data on animal muscle and those on human parallel-fibred muscle.

Effect of aging on human adductor pollicis muscle function

The effect of aging on the voluntary and electrically evoked contractile properties of the human adductor pollicis muscle was investigated in 70 healthy male subjects aged 20-91 yr, 10 subjects for each decade. Maximum isometric voluntary force declined significantly (range of P values less than 0.001-0.05) after the age of 59 yr, dropping by the eighth decade to 57.6% of the level recorded in the second decade. A significant shift (P range less than 0.001-0.05) to the left of the frequency-force curve after ulnar nerve supramaximal stimulation at 1, 10, 20, 30, and 50 Hz was observed in the most elderly group (greater than 80 yr) compared with the youngest group (20-29 yr). Maximum relaxation rate dropped by 48.7% from the second to the eighth decade. The decrease became significant (P range less than 0.05-0.001) with the sixth decade. Isometric endurance, evaluated during 30 s of stimulation at 30 Hz, showed a linear (P less than 0.001) increase with age. Aged muscle is thus weaker, slower, and tetanized at lower fusion frequencies but, paradoxically, more resistant to static fatigue.

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)