Aerobic capacity and skeletal muscle properties of normoxic and hypoxic rats in response to training

The aim of this study was to determine, in the rat, the effects of chronic exposure (7–9 weeks) to normobaric hypoxia (FIO₂ = 0.13, equivalent to 3700 m altitude) on cardiac and skeletal muscle properties, on maximal oxygen uptake (VO_2max), and endurance time to exhaustion (ETE). In addition, we evaluated the impact of endurance training (90 min of treadmill running per day, 5 days per week, for 9 weeks) on these parameters. The results were compared to normoxic rats fed ad libitum (N_AL) and to normoxic pair-weight (N_PW) animals in order to take into account the influence of hypoxia on growth rate. It was found that, in sedentary rats, hypoxia results in stunted growth, adrenal atrophy, a significant reduction of cross-sectional area of fast-twitch (type II) fibres, a reduced capillary-to-fibre ratio (C/F), and a reduced oxidative capacity (decreases in citrate synthase and 3-hydroxy-Acyl CoA dehydrogenase activities) of the plantaris muscle. These effects are mainly related to the anorexic effects of prolonged exposure to hypoxia. Nevertheless, hypoxic (H) rats displayed higher VO_2max and ETE values when compared either to N_AL or to N_PW animals. Endurance training resulted, in all groups (H, N_AL, N_PW), in a significant change of the fibre type distribution of the plantaris which displayed an increased number of type IIA fibres and a decreased proportion of type IIB fibres. In addition, the C/F ratio and cross-sectional area of fast-twitch fibres were normalized by superimposition of training on hypoxia. Both VO_2max and ETE were significantly higher in trained H rats than in N_AL, but these improvements were mainly related to the reduced body weight induced by hypoxia. These data suggest that the greater aerobic capacity and tolerance for prolonged exercise induced by chronic exposure to hypoxia can be mainly accounted for by the anorexic effects of hypoxia, although other factors (e.g. increase in oxygen carrying capacity induced by hypoxia acclimatization) may play a significant role in some circumstances (e.g. in sedentary rats). Received: 30 March 1995/Received after revision: 30 August 1995/Accepted: 4 September 1995     

Body composition,fitness, and metabolic health during strength and endurance training and their combination in middle-aged and older women

In this study adaptations in body composition, physical fitness and metabolic health were examined during 21 weeks of endurance and/or strength training in 39- to 64-year-old healthy women. Subjects (n = 62) were randomized into endurance training (E), strength training (S), combined strength and endurance training (SE), or control groups (C). S and E trained 2 and SE 2 + 2 times in a week. Muscle strength and maximal oxygen uptake (VO₂max) were measured. Leg extension strength increased 9 ± 8% in S (P < 0.001), 12 ± 8% in SE (P < 0.001) and 3 ± 4% in E (P = 0.036), and isometric bench press 20% only in both S and SE (P < 0.001). VO₂max increased 23 ± 18% in E and 16 ± 12% in SE (both P < 0.001). The changes in the total body fat (dual X-ray absorptiometry) did not differ between groups, but significant decreases were observed in E (−5.9%, P = 0.022) and SE (−4.8%, P = 0.005). Lean mass of the legs increased 2.2–2.9% (P = 0.004–0.010) in S, SE and E. There were no differences between the groups in the changes in blood lipids, blood pressure or serum glucose and insulin. Total cholesterol and low-density lipoprotein cholesterol decreased and high-density lipoprotein cholesterol increased in E. Both S and SE showed small decreases in serum fasting insulin. Both endurance and strength training and their combination led to expected training-specific improvements in physical fitness, without interference in fitness or muscle mass development. All training methods led to increases in lean body mass, but decreases in body fat and modest improvements in metabolic risk factors were more evident with aerobic training than strength training.     

Phosphorus-31 nuclear magnetic resonance study on the effects of endurance training in rat skeletal muscle

Summary To evaluate changes in muscle energetics following endurance training, we measured phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectra on rat muscle in vivo before and after training in the same animals. The endurance training lasted for 3 months. The³¹P NMR spectra were obtained serially at rest, during exercise by electrical stimulation, and during recovery. Intramuscular phosphocreatine (PCr), inorganic phosphate (P_i, adenosine 5-triphosphate (ATP) and pH were determined from the NMR spectra. The ratio of PCr : (PCr + P_i) at rest showed no difference between the trained and control groups even after 3 months of training. During exercise, however, this ratio was significantly higher in the trained group than in the control group. The ratio also recovered more rapidly after exercise in the trained group. The intramuscular pH decreased slightly by approximately 0.1 pH unit during exercise but did not show a significant difference between the groups. These results indicated that endurance training of 3 months duration improved the ATP supply system in the muscle. They also demonstrated that³¹P NMR is a potent method for evaluating the effects of training in the same individuals.     

Effects of intensified endurance training on the concentration of Na,K-ATPase and Ca-ATPase in human skeletal muscle

Thirty-nine moderately endurance trained males increased their normal training programme of 2.2 h week^-1 with an average training intensity of 65 % of maximum heart rate (HR_max) to 2.7 h week^-1 and a mean intensity of 78% of HR_max. Performance tests and measurements of the total concentrations of Na,K-ATPase (³H-ouabain binding) and Ca-ATPase, fibre type distribution and fibre area were performed in biopsies from the vastus lateralis muscle before and after increased training. The 6 weeks of training elevated Vo_2max from 54.9 + 3.1 to 58.3±3.0 ml 0₂ min^-1 kg^-1 (P < 0.0001). Exercise time to exhaustion at 86% of Fo_2max (pre-training) increased from 35 ±8 to 61 + 17 min (P < 0.0001). The concentration of Ca-ATPase was unaffected by the intensified training (6.74 ± 1.03 vs. 6.68+ 1.07 nmol g wet wt^-1), but the concentration of Na,K-ATPase increased from 307±43 to 354 + 59 pmol g wet wt ' (P < 0.0001). The relative distribution of FT-fibres was correlated with the concentration of Ca-ATPase (r = 0.72, P < 0.0001). The data support the view that intensive training induces an upregulation of the concentration of skeletal muscle Na,K-ATPase, but no change in the total capacity for reaccumulation of Ca²⁺ into the SR. There was no correlation between the concentrations of Na,K-ATPase, Ca-ATPase and indices of endurance performance.     

The effect of varying the time of concentric and eccentric muscle actions during resistance training on skeletal muscle adaptations in women

This study investigated the effect of manipulating the time to complete both the concentric (CON) and eccentric (ECC) muscle actions during resistance training on strength, skeletal muscle properties and cortisol in women. Twenty-eight women (mean ± SE age = 24.3 ± 1.1 year) with strength training experience completed three training sessions per week for 9 weeks. Two sets of four lower body exercises (leg press, parallel squat, knee extension and knee flexion) were completed using 6–8 RM intensity. The long CON (LC) group performed the CON action for 6 s and the ECC action for 2 s, while the long ECC (LE) group completed the CON and ECC phases for 2 and 6 s, respectively. Both groups experienced significant increases in leg press CON only, ECC only and combined ECC and CON maximal strength (1 RM). Immunohistochemical analyses demonstrated that both types I and IIA vastus lateralis fibre areas significantly increased following LC training while only type I fibre area increased following LE training. There was a decrease in MHCIId(x) with a concomitant increase in MHCIIa (P < 0.05) in both groups. Twenty-four hour urinary cortisol significantly increased after LC training only. It was concluded that LC resistance training was more effective than LE for increasing both types I and IIA fibre area and cortisol when time under tension and intensity of muscle actions were matched between the two modes of resistance training in young healthy women.     

Skeletal muscle enzyme activity,fiber composition and \dot VO2 max in relation to distance running performance

Summary Muscle biopsy samples were obtained from the gastrocnemius of 26 well-trained runners of widely varying ability. Portions of the sample were analyzed for succinate dehydrogenase (SDH) activity and for muscle fiber composition. O₂ max was determined during uphill treadmill running. Mean values for muscle SDH activity (14.6 U/g), fiber composition (55% slow twitch) and O₂ max (60.9 ml/kg×min^–1) were lower than reported previously for groups of elite and sub-elite runners. The physiological data were consistent with the performance ability of the sample [512, 1120 and 3640 (mins) for 1, 2 and 6 miles, respectively]. Within the sample, performance was most strongly related to O₂ max (r=–0.84, –0.87 and –0.88 for 1, 2, and 6 miles). There was little relationship between muscle SDH activity and either performance (r=–0.11, –0.14, –0.20 for 1, 2, and 6 miles) or O₂ max (r=0.23). The relationship between muscle fiber composition and performance was only modestly strong (r=–0.52, –0.54, –0.55 for 1, 2, and 6 miles). The results indicate that the primary determinant of cross-sectional differences in running performance is O₂ max. Skeletal muscle metabolism apparently contributes little to these cross-sectional differences and may be of much greater importance to variations in performance within an individual.     

Relationships between muscle strength and muscle cross-sectional area in male sprinters and endurance runners

Summary The relationship between the cross-sectional area (CSA) and maximum voluntary isometric strength of the knee extensor muscles was measured in a group of untrained subjects (control group, n=30), a group of successful marathon runners (n=6) and a group of successful sprinters (n=6). All subjects were male, aged between 20 and 41 years. In the control group muscle strength was found to be positively correlated with lean body mass (p<0.01) and with muscle CSA as determined by computed tomography scanning of the leg at mid-thigh level (p<0.001). However, in spite of these significant relationships, there was considerable variability between subjects. The sprinters were significantly stronger than the endurance runners (p<0.01), but neither of the athletic groups differed significantly from the control group. Muscle CSA was greater in the sprinters than in the marathon runners but this difference was not significant. The ratio of muscle strength to CSA in the control group varied from 7.07 to 13.57. All the trained subjects fell within this normal range, but the sprinters' muscles were stronger per unit CSA than the muscles of the marathon runners (p<0.05). Since it is well established that the leg muscles of sprinters contain a high proportion of fast twitch (FT) muscle fibres whereas endurance runners have a high proportion of slow twitch (ST) fibres, these results suggest that the strength which can be produced by a muscle may depend on its fibre composition. Variation in the distribution of the different fibre types in the untrained population may therefore account at least in part for the wide variability observed in this group.Supported by a grant from Lipha Pharmaceuticals Ltd     

Relationships between skeletal muscle characteristics and aerobic performance in sedentary and active subjects

Summary Forty-eight sedentary and 39 quite active or well-trained men participated in this study. Muscle biopsy samples were taken from the vastus lateralis for the determination of fiber type composition (I, IIa, IIb), fiber type area, and assay of the following enzymes: malate dehydrogenase (MDH), 3-hydroxyacyl CoA dehydrogenase (HADH) and oxoglutarate dehydrogenase (OGDH). Maximal oxygen uptake ( ) was determined with a progressive cycle ergometer test, while endurance performance or maximal aerobic capacity (MAC) was defined as the total work output during a 90-min cycle ergometer test. Correlation analysis revealed no evidence of association between fiber type composition and kg^–1 or MAC kg^–1 in sedentary subjects, while active men exhibited significant correlation between % type I (r=0.52), % type IIb (r=–0.31) and kg^–1. Enzyme activities were not significantly correlated with MAC kg^–1 and kg^–1 in sedentary men while active men exhibited significant correlation for the three enzymes (0.37r0.51) with kg^–1. These results show that the contribution of muscle fiber type and enzyme activities to aerobic performance may be inflated from a statistiscal point of view by the training status heterogeneity of subjects. They also suggest that variation in these muscle characteristics does not account for the individual differences in aerobic performance of subjects who have never trained before. Therefore, the assessment of muscle characteristics is not as useful as originally thought for the detection of individuals with a high potential for endurance performance among untrained subjects.     

Effect of strength training on the relationship between magnetic resonance relaxation time and muscle fibre composition

Summary The effect of muscle hypertrophy on the relationship between magnetic resonance (MR) relaxation time and muscle fibre composition was investigated. Relaxation time and muscle fibre composition were measured in five subjects before and after a 20-week period of strength training. Muscle fibre composition in all subjects exhibited a significant shift to a predominance of fast-twitch (FT) fibres as a result of 20-week strength training (% area FT fibres: mean values from 49.8%, SD 17.9% to 57%, SD 5.6%; P<0.05). Longitudinal relaxation time (T₁) and transverse relaxation time (T₂) were prolonged significantly after strength training (T₁ mean values from 334.9 ms, SD 13.6 to 359.0 ms, SD 9.0, P<0.001; T₂ from 27.5 ms, SD 0.9 to 30.8 ms, SD 2.3, P<0.05). A constant relationship was observed in changes caused by strength training in muscle fibre composition (% area FT) and relaxation time, with a high correlation obtained between both parameters. These results indicate that MR relaxation time can be used for non-invasive estimation of muscle fibre composition.     

Physical work capacity in dynamic exercise with differing muscle masses in healthy young and older men

Ten young (aged 23–30 years) and nine older (aged 54–59 years) healthy men with similar estimated limb muscle volumes performed, in random order, three different types of ergometer exercise tests (one-arm cranking, two-arm cranking, and two-leg cycling) up to the maximal level. Values for work load (WL), peak oxygen consumption , peak heart rate (HR), peak ventilation , respiratory gas exchange ratio (R), recovery blood lactate concentration [La^–], and rating of perceived exertion (RPE) were compared between the age-groups in the given exercise modes. No significant age-related differences in WL, peak , peak HR, R, [La^–], or RPE were found in one-arm or two-arm cranking. During one-arm cranking the mean peak was 1.65 (SD 0.26)1 · min^–1 among the young men and 1.63 (SD 0.10)1 · min^–1 among the older men. Corresponding mean peak during two-arm cranking was 2.19 (SD 0.32)1 · min-1 and 2.09 (SD 0.18)1 · min^–1, respectively. During one-arm cranking peak was higher (P < 0.05) among the older men compared to the young men. During two-leg cycling the young men showed higher values in WL (P < 0.001), peak (P < 0.001), and peak HR (P < 0.001). The mean peak was 3.54 (SD 0.24)1 · min^–1 among the young men and 3.02 (SD 0.20)1 · min^–1 among the older men. Corresponding mean peak HR was 182 (SD 5) beats · min^–1 and 170 (SD 8) beats · min^–1, respectively. During two-leg cycling, peak , R, [La^–], and RPE did not differ between the two age-groups. In summary, the older men with similar sizes of estimated arm and leg muscle volumes as the young men had a reduced physical work capacity in two-leg cycling. In one-arm or two-arm cranking, no significant difference in work capacity was found between the age-groups. These results indicate, that in healthy men, age, at least up to the 6th decade of life, is not necessarily associated with a decline in physical work capacity in exercises using relatively small muscle groups, in which the limiting factors are more peripheral than central.     

Effects of age and regular exercise on muscle strength and endurance

Summary Twenty male and 20 female non-professional tennis players were classified into two different age groups (n=10 per group): young active men (30.4±3.3 years), young active women (27.5±4.3 years), elderly active men (64.4±3.7 years), and elderly active women (65.3±4.5 years). These individuals were matched (n = 10 per group) according to sex, age, height and mass to sedentary individuals of the same socio-economical background: young sedentary men (29.2±3.4 years), young sedentary women (25.6±4.4 years), elderly sedentary men (65.2 ± 3.2 years) and elderly sedentary women (65.6±4.4 years). An isokinetic dynamometer was used to measure the strength of the knee extensors and flexors (two separate occasions) and the endurance of the extensors. Vastus lateralis electromyogram (EMG) was measured concomitantly. Significant sex, age and exercise effects (P<0.001) were observed for peak torque of both muscle groups. The effect of age on extensor strength was more pronounced at high speeds where men were also able to generate larger relative torques than women.No age or sex effects were noted for muscle endurance. However, muscles of active individuals demonstrated a greater resistance to fatigue than those of sedentary individuals. In conclusion, men were found to be stronger than women, age was associated with a decrease in muscle strength, but not of muscle endurance, and tennis players were stronger and had muscles that were more resistant to fatigue than their sedentary pairs in both age groups. Although the results of this study cannot be generalized to other types of sports activities, they do give credence to the health benefits of moderate exercise in the maintenance of muscle function with age.     

Effects of ageing and endurance exercise training on alpha-actinin isoforms in rat plantaris muscle

Aim: We recently reported that α‐actinin adaptation occurs at the isoform level. This study was undertaken to clarify the effects of: (1) ageing‐induced shift of myosin heavy chain (MyHC) composition and (2) endurance exercise training on α‐actinin isoforms in rat plantaris muscle. Methods: Adult (18 mo) and old (28 mo) male Fischer 344 rats were assigned to either sedentary control or endurance exercise training groups. Animals in the training groups ran on a treadmill for 8 week with training intensity adjusted to be equal for adult and old groups. After the training was completed, the plantaris muscles were taken for analyses of α‐actinin‐2, α‐actinin‐3, and MyHC composition and metabolic enzyme activities. Results: The proportion of type IIb MyHC was lower, and that of type I MyHC was higher in old animals than in adult animals. α‐actinin‐3 was significantly lower in old animals than in adult animals. No significant difference was found in α‐actinin‐2 and citrate synthase (CS) activity between adult and old animals. Citrate synthase activity was higher in trained animals than in sedentary animals. Endurance training produced a fast‐to‐slow shift within type II MyHC isoforms in both adult and old animals. α‐actinin‐2 was significantly higher in trained animals than in sedentary animals. No significant difference was found in α‐actinin‐3 between trained and sedentary animals. Conclusion: These results support the α‐actinin adaptation at the isoform level and show that the α‐actinin‐3 expression depends on the amount of type II MyHC, whereas α‐actinin‐2 expression is associated with improvement of muscular aerobic capacity.     

Physiological and muscle enzyme adaptations to two different intensities of swim training

Summary To test the hypothesis that a smaller quantity of high intensity (HI) as opposed to a larger quantity of moderate intensity (MI) swim training would result in adaptations more specific to the short performance times of swimming competitions, two groups of elite university swimmers were tested before and after 6.5 weeks of specific HI or MI intermittent swim training. In training, swimming times were faster and blood lactate concentrations were higher (10.2 vs. 7.5 mM) during HI compared to MI training. No significant differences were observed between the two groups for any of the variables measured, before or after training. However, significant increases with training were observed for the activities of hexokinase, phosphorylase, phosphofructokinase, succinate dehydrogenase, and 3-hydroxyacyl CoA dehydrogenase in the deltoid, but not the gastrocnemius muscles. Training resulted in significant increases in O₂ max during treatmill running, but not during tethered swimming. It is concluded that a larger quantity of MI swim training results in physiological adaptations that are similar to those obtained with a smaller quantity of HI training, at least over a relatively short training period.This study was supported by a grant from the Natural Sciences and Engineering Research Council of Canada     

Effect of hind-limb immobilization on contractile and histochemical properties of skeletal muscle

Summary Both hind limbs of male rats were immobilized in casts. After 4 weeks, serial sections of hind limb muscles were stained for myosin ATPase and NADH-diaphorase. The soleus from immobilized limbs had significantly fewer muscle fibers than the control soleus. Moreover, the soleus from immobilized limbs had a significantly lower percentage and lower number of fibers with low myosin ATPase activity than the soleus from control rats. Immobilization also resulted in the speed of contraction for the soleus being significantly faster than the soleus from control rats. There were no significant differences in the contractile properties or in the percentages of fibers with low myosin ATPase between rectus femoris muscles from immobilized and control limbs. The deep portion of the rectus femoris from immobilized limbs had a significantly smaller percentage of muscle fibers with high NADH-diaphorase activity than did the rectus femoris from control rats.The animals involved in this study were maintained in accordance with the Guide for Laboratory Animal Facilities and Care as published by the National Academy of Sciences-National Research Council.The research reported in this paper was conducted by personnel of the Environmental Sciences Division, USAF School of Aerospace Medicine, Aerospace Medical Division, AFSC, Brooks AFB, Texas. Further reproduction is authorized to satisfy the needs of the U.S. Government.     

Muscle fibre type distribution,muscle cross-sectional area and maximal voluntary strength in humans

The relationship between maximum voluntary concentric strength, muscle fibre type distribution and muscle cross-sectional areas were examined in 23 subjects (7 female and 11 male phys. ed. students as well as 5 male bodybuilders). Maximal knee and elbow extension as well as elbow flexion torque at the angular velocities 30, 90 and 180 degrees per second was measured. Muscle biopsies were taken from vastus lateralis and m. triceps brachii. The muscle cross-sectional area of the thigh and upper arm was measured with computed tomography scanning. The maximal torque correlated strongly to the muscle cross-sectional area times an approximative measure on the lever arm (body height). Maximal tension developed per unit of muscle cross-sectional area did not correlate significantly with per cent type I fibre area and did not differ between the female and male students or bodybuilders. Neither did the relative decrease in torque with increasing contraction velocity show any significant relationship to the per cent type I fibre area. The total number of muscle fibres was estimated by dividing the muscle cross-sectional area with the mean fibre area of m. triceps brachii. The number of fibres did not seem to differ between the sexes.     

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.     

Influences of endurance training on the ultrastructural composition of the different muscle fiber types in humans

To investigate changes in the ultrastructure of the different muscle fiber types induced by endurance training ten sedentary subjects (five women and five men) were exercised on bicycle ergometers 5 times a week for 30 min. After 6 weeks of training there were significant changes in (+14%), in the percentage of type I (+12%) and type IIB fibers (–24%) as well as in the volume densities of mitochondria. The latter increased 35% in type I, 55% in type IIA and 35% in type IIB fibers. The relative increase in subsarcolemmal mitochondria was larger than in interfibrillar mitochondria in all fiber types. There was also a significant increase in the volume density of intracellular lipid in type II fibres. It is concluded that high intensity endurance training leads to an enhancement of the oxidative capacity in all muscle fiber types.     

Post-exercise leg and forearm flexor muscle cooling in humans attenuates endurance and resistance training effects on muscle performance and on circulatory adaptation

The influence of regular post-exercise cold application to exercised muscles trained by ergometer cycling (leg muscles) or handgrip exercise using a weight-loaded handgrip ergometer (forearm flexor muscles) was studied in human volunteers. Muscle loads were applied during exercise programs three to four times a week for 4–6 weeks. Besides measuring parameters characterizing muscle performance, femoral and brachial artery diameters were determined ultrasonographically. Training effects were identified by comparing pre- and post-training parameters in matched groups separately for the trained limbs cooled after exercise by cold-water immersion and the corresponding trained limbs kept at room temperature. Significant training effects were three times more frequent in the control than in the cold group, including increases in artery diameters in the control but not in the cold group. It is concluded that training-induced molecular and humoral adjustments, including muscle hyperthermia, are physiological, transient and essential for training effects (myofiber regeneration, muscle hypertrophy and improved blood supply). Cooling generally attenuates these temperature-dependent processes and, in particular, hyperthermia-induced HSP formation. This seems disadvantageous for training, in contrast to the beneficial combination of rest, ice, compression and elevation in the treatment of macroscopic musculo-tendinous damage. Part of the results were presented at the Congress on Physiology and Pharmacology of Temperature Regulation held in Rhodes (Greece) in October 14, 2004 [Ohnishi N, Yamane M, Uchiyama N, Shirasawa S, Kosaka M, Shiono H, Okada T (2004) Adaptive changes in muscular performance and circulation by resistance training with regular cold adaptation. J Therm Biol 29: 839–843].     

Changes in contractile properties of muscle after strength training in man

Summary Thirty young male adults matched in two experimental groups (n=12) and a control group (n=6) were investigated before and after an 8-week strength training period. Group A trained with few repetitions and maximal loads, whereas group B had more repetitions with smaller loads. Both groups lifted the same total load during each training period, four times a week. Maximal voluntary strength (MVS) of a shot-put arm movement, muscular excitability and contractile properties (time to peak of contraction with threshold stimuli, half relaxation time) were measured in M. deltoideus and M. triceps brachii, C. longum, for two durations of stimulation. Increases of 14.8% (group A) and 12.2% (group B) in MVS were observed. Muscle excitability significantly increased in all types of training and both muscles. Significant shortening of the contraction time, dependent on the type of training, was observed in both studied muscles. It appears that the strength training in group A involved the fast fibers of both muscles, whereas in group B the training influence was less marked, and affected both fast and slow fiber types.     

Cardiovascular and muscular adaptations to combined endurance and strength training in elderly women

Twenty-one women aged 60–75 years were examined to determine whether combined endurance and strength training resulted in greater increase in peak oxygen consumption, sub-maximal time to fatigue, cardiac output, stroke volume, and leg extension load when compared to endurance training alone. Subjects in both the endurance training (E) and endurance and strength (E & S) groups trained 3 days a week, for 12 weeks, at an intensity of 70–80% V˙O ₂ peak for 30 min on a cycle ergometer. Subjects in the E & S groups also used resistance equipment to train the knee extensors. The workload for resistance training was based on an initial assessment of 10 repetitions maximum (10 RM), with 80% of that value used for training, three times weekly. Peak oxygen consumption increased to an average of 24.8 and 29.9% in the E and E & S groups, respectively, with no difference between groups. Subjects in the E & S and E groups significantly increased sub-maximal endurance time by 396 and 165%, respectively. Cardiac output, stroke volume, and arteriovenous oxygen difference at 80% peak V˙O ₂ were unchanged by either of the training methods. A needle biopsy was taken from the vastus lateralis before and after 12 weeks of training. Chi-square analysis of fibre area data showed an increase in the frequency of larger type I fibres in the post-training data from the E & S group, but an increase in the frequency of smaller fibres in the E group post-training; however, mean fibre area was not significantly changed by training. These data suggest that greater improvements in sub-maximal time to fatigue and strength is achieved when resistance training is added to an aerobic training programme in healthy elderly women.