Muscle hypertrophy following 5‐week resistance training using a non‐gravity‐dependent exercise system

Aim: The efficacy of a mechanical, gravity‐independent resistance exercise (RE) system to induce strength gains and muscle hypertrophy was validated. Designed for space crew in orbit, this technique offers resistance during coupled concentric and eccentric actions by utilizing the inertia of a rotating flywheel(s), set in motion by the trainee. Methods: Ten middle‐aged (30–53 years) men and women performed four sets of seven maximal, unilateral (left limb) knee extensions two or three times weekly for 5 weeks. Knee extensor force and electromyographic (EMG) activity of the three superficial quadriceps muscles were measured before and after this intervention. In addition, with the use of magnetic resonance imaging (MRI), volume of individual knee extensor and ankle plantar flexor muscles was assessed. Results: Over the 12 training sessions, the average concentric (CON) and eccentric (ECC) force generated during exercise increased by 11% (P < 0.05). Likewise, maximal isometric strength (maximal voluntary contraction, MVC) at 90 and 120° knee angle increased by (P < 0.05) 11 and 12% respectively, after training. Neither individual quadriceps muscle showed a change (P > 0.05) in maximal integrated EMG (iEMG) activity. Quadriceps muscle volume increased by 6.1% (P < 0.05). Although the magnitude of response varied, all individual quadriceps muscles showed increased (P < 0.05) volume after training. As expected, ankle plantar flexor volume of the trained limb was unchanged (P > 0.05). Likewise, MVC, CON and ECC force, iEMG and knee extensor and plantar flexor muscle volume were unaltered (P > 0.05) in the right, non‐trained limb. Conclusion: The results of this study show that the present RE regimen produces marked muscle hypertrophy and important increases in maximal voluntary strength and appears equally effective as RE paradigms using gravity‐dependent weights, in this regard.     

The contribution of muscle hypertrophy to strength changes following resistance training

Purpose

Whilst skeletal muscle hypertrophy is considered an important adaptation to resistance training (RT), it has not previously been found to explain the inter-individual changes in strength after RT. This study investigated the contribution of hypertrophy to individual gains in isometric, isoinertial and explosive strength after 12 weeks of elbow flexor RT.

Methods

Thirty-three previously untrained, healthy men (18–30 years) completed an initial 3-week period of elbow flexor RT (to facilitate neurological responses) followed by 6-week no training, and then 12-week elbow flexor RT. Unilateral elbow flexor muscle strength [isometric maximum voluntary force (iMVF), single repetition maximum (1-RM) and explosive force], muscle volume (V _m), muscle fascicle pennation angle (θ _p) and normalized agonist, antagonist and stabilizer sEMG were assessed pre and post 12-week RT.

Results

Percentage gains in V _m correlated with percentage changes in iMVF (r = 0.527; P = 0.002) and 1-RM (r = 0.482; P = 0.005) but not in explosive force (r ≤ 0.243; P ≥ 0.175). Percentage changes in iMVF, 1-RM, and explosive force did not correlate with percentage changes in agonist, antagonist or stabilizer sEMG (all P > 0.05). Percentage gains in θ _p inversely correlated with percentage changes in normalized explosive force at 150 ms after force onset (r = 0.362; P = 0.038).

Conclusions

We have shown for the first time that muscle hypertrophy explains a significant proportion of the inter-individual variability in isometric and isoinertial strength gains following 12-week elbow flexor RT in healthy young men.     

Adaptations in rat skeletal muscle following long-term resistance exercise training

The purpose of this investigation was to determine whether long-term, heavy resistance training would cause adaptations in rat skeletal muscle structure and function. Ten male Wistar rats (3 weeks old) were trained to climb a 40-cm vertical ladder (4 days/week) while carrying progressively heavier loads secured to their tails. After 26 weeks of training the rats were capable of lifting up to 800?g or 140% of their individual body mass for four sets of 12–15 repetitions per session. No difference in body mass was observed between the trained rats and age-matched sedentary control rats. Absolute and relative heart mass were greater in trained rats than control rats. When expressed relative to body mass, the mass of the extensor digitorum longus (EDL) and soleus muscles was greater in trained rats than control rats. No difference in absolute muscle mass or maximum force-producing capacity was evident in either the EDL or soleus muscles after training, although both muscles exhibited an increased resistance to fatigue. Individual fibre hypertrophy was evident in all four skeletal muscles investigated, i.e. EDL, soleus, plantaris and rectus femoris muscles of trained rats, but muscle fibre type proportions within each of the muscles tested remained unchanged. Despite an increased ability of the rats to lift progressively heavier loads, this heavy resistance training model did not induce gross muscle hypertrophy nor did it increase the force-producing capacity of the EDL or soleus muscles.     

Muscle metabolite accumulation following maximal exercise

Summary Five elite flatwater kayak paddlers were studied during indoor simulated 500 and 10,000-m races, with performance times of 2 and 45 min, respectively. Muscle biopsies were obtained from the midportion of m. deltoideus immediately pre and post exercise. Concentrations of adenosine triphosphate (ATP), creatine phosphate (CP), glucose, glucose-6-phosphate (G-6-P), glycogen, and lactate were subsequently determined. Short term exercise resulted in statistically significant increases in glucose (P<0.001), G-6-P (P<0.05) and lactate (P<0.01) concentration concomitant with decreased CP (P<0.05) and glycogen (P<0.01). Following prolonged exercise, a non-significant elevation in glucose and a reduction (P<0.01) in glycogen were demonstrated.Evidently the metabolic demands for kayak competitions at 500 and 10,000 m are different. Thus, the energy contribution from glycolytic precursors and the anaerobic component is of greater relative importance in short distances than in exercise of long duration. A generalization of the findings to other athletic events of varying distances is proposed. The present data on arm-exercise is consistent with previous findings obtained in connection with leg exercises.     

Variable resistance training promotes greater fatigue resistance but not hypertrophy versus constant resistance training

Loading using variable resistance devices, where the external resistance changes in line with the force:angle relationship, has been shown to cause greater acute neuromuscular fatigue and larger serum hormone responses. This may indicate a greater potential for adaptation during long-term training. Twelve (constant resistance group) and 11 (variable resistance group) men completed 20 weeks of resistance training with 10 men as non-training controls. Training-induced adaptations were assessed by bilateral leg press one repetition maximum, a repetition to failure test using 75 % 1RM, lower limb lean mass and vastus lateralis cross-sectional area. Only the variable resistance training group improved the total number of repetitions (41 ± 46 %) and volume load (52 ± 37 %) during the repetition to failure test (P < 0.05). Similar improvements in maximum strength and hypertrophy of the lower limbs were observed in both training groups. Also, constant and variable resistance 5 × 10RM leg press loadings were performed before and after training in a crossover design. Acute loading-induced responses were assessed by concentric and isometric force, serum hormone concentrations and phosphorylation of intramuscular signalling proteins (0–30 min post-loading). Greater acute decreases in force (P < 0.05–0.01), and greater increases in serum testosterone and cortisol concentration (P < 0.05) and ERK 1/2 phosphorylation (P < 0.05) were observed following variable resistance loadings before and after training. Greater training-induced improvements in fatigue resistance occurred in the variable resistance training group, which may be due to greater acute fatigue and physiological responses during variable versus constant resistance loadings.     

Neuromuscular adaptations following 12-week maximal voluntary co-contraction training

Purpose

The present study examined neuromuscular adaptations following 12-week maximal voluntary co-contraction training.

Methods

Sixteen young men were allocated to training (TG, n = 9) or control (CG, n = 7) group. TG conducted a training program (3 days/week), which consisted of 4-s maximal voluntary contractions of elbow flexors and extensors by simultaneously contracting both muscle groups at 90° of the elbow joint, followed by 4-s muscle relaxation (10 repetitions/set, 5 sets/day) for 12 weeks. In addition to the muscle thicknesses of elbow flexors and extensors, the torque and electromyograms (EMGs) of the two muscle groups during isometric maximal voluntary contraction (MVC) were determined before (Pre), after 4 weeks, and 12 weeks of intervention.

Results

After intervention, CG showed no significant changes in all measured variables. In TG, MVC torque significantly increased in both elbow flexors (+13 % at 4 weeks and +15 % at 12 weeks) and extensors (+27 % at 4 weeks and +46 % at 12 weeks) from Pre. Muscle thickness also significantly increased in both elbow flexors (+4 %) and extensors (+4 %) at 12 weeks. Agonist EMG activities during MVC significantly increased in both elbow flexors (+31 % at 4 weeks and +44 % at 12 weeks) and extensors (+27 % at 4 weeks and +40 % at 12 weeks), without changes in antagonist involuntary coactivation level in both muscle groups.

Conclusion

These results indicate that maximal voluntary co-contraction is applicable as a training modality for increasing the size and strength of antagonistic muscle pairs without increasing involuntary coactivation level.     

Association between regional differences in muscle activation in one session of resistance exercise and in muscle hypertrophy after resistance training

The purpose of this study was to examine if the regional difference in muscle hypertrophy after chronic resistance training is associated with muscle activation after one session of resistance exercise. Twelve men performed one session of resistance exercise of elbow extensors. Before and immediately after the exercise, transverse relaxation time (T2)-weighted magnetic resonance (MR) images of upper arm were recorded to evaluate the muscle activation along its length. In the MR images, T2 for the pixels within the triceps brachii muscle was quantified. The number of pixels with T2 greater than the threshold (mean + 1SD of T2 before the exercise) was expressed as the ratio to the number of pixels occupied by the muscle (%activated area). Another 12 subjects completed 12 weeks of training intervention (3 days per week), which consisted of the same program variables as used in the experiment for the T2 measurement. The cross-sectional areas of the triceps brachii before and after the training intervention were measured from MR images of upper arm. The %activated area of the triceps brachii induced by one session of the exercise was found to be significantly lower in the distal region than the middle and proximal regions. Similarly, the relative increase in muscle cross-sectional area after the 12 weeks of training intervention was significantly less in the distal region than the middle and proximal regions. The results suggest that the regional difference in muscle hypertrophy after chronic resistance training is attributable to the regional difference in muscle activation during the exercise.     

Muscle adaptation prior to recovery following eccentric exercise

Summary The effects of performing a second eccentric exercise bout prior to and after recovery from the first bout were compared. Twenty subjects performed 70 eccentric actions with the forearm flexors. Group A (n = 9) and group B (n = 11) repeated the same exercise 5 and 14 days after the initial bout, respectively. Dependent variables included muscle soreness, elbow joint angles, isometric strength, and serum creatine kinase (SCK). Subjects were tested pre-exercise and up to day 5 following each bout. The first bout produced significant changes in all measures for both groups (P < 0.01). Values remained significantly different from baseline on day 5 when group A repeated the exercise (P < 0.01) but were back to normal when group B performed bout 2. For both groups an adaptation occurred; significantly smaller changes in dependent variables were produced by the second bout, and recovery time was faster whether or not muscles were fully restored (P < 0.01). The repeated bout did not exacerbate soreness, performance decrements, and elevation of SCK when performed by affected muscles that had not fully recovered from the first bout. Thus, the results suggest that an adaptation response had taken place prior to full recovery and restoration of muscle function following the initial eccentric exercise bout.     

Sympathetic nervous system and behavioral responses to stress following exercise training.

This study tests the hypothesis that a short-term (16 weeks) exercise program modifies sympathetic nervous system (SNS) and selected behavioral responses to acute psychological stress. Twenty-four previously sedentary middle-aged men with maximal aerobic capacity (VmaxO2) values less than 40 ml.kg-1.min-1 were assigned to experimental (n = 12) and control (n = 12) groups. All subjects performed a modified Stroop test (18 min) at pre- and postexercise training during which intravenous blood samples were drawn at three time intervals for plasma catecholamine (CA) determination. Motor performance was continuously recorded for assessment of premotor (PMT) and motor (MOT) components of reactions time. A set of anagrams were administered immediately following the modified Stroop to determine the level of cognitive fatigue induced. At both pre- and postexercise intervention, the total group (n = 24) manifested significant (p less than or equal to 0.05) elevations in state anxiety, heart rate, and plasma norepinephrine. No significant changes occurred over time on PMT or MOT. There were significantly (p less than or equal to 0.01) lengthened anagram performance scores poststress compared to nonstress values. The experimental group exercise trained 3 days/week for 16 weeks, resulting in a 20% increase in VO2max. However, there were no group differences on the CA or behavioral responses to the modified Stroop at pre- or postintervention. These findings do not support the hypothesis that short-term aerobic training significantly alters SNS activity or behavioral measures of central processing in middle-aged men exposed to an acute psychological challenge.     

Muscle protein changes following eccentric exercise in humans

Summary This study characterized changes in the protein composition of human muscle tissue after eccentric exercise. Four subjects performed 70 maximum eccentric, isokinetic actions of the forearm flexors with one arm. The other arm served as control. A biopsy of the biceps muscle of each arm was taken 2 days after exercise when muscles were very sore (mean = 8.0; 1 = normal; 10 = very, very sore), and muscle damage was documented by a mean decrease of 0.2 radians in the relaxed elbow angle. Proteins from the biopsy tissue were solubilized in a high ionic strength buffer containing several proteolytic inhibitors. Protein concentrations of the extracts were determined and identical amounts loaded onto sodium dodecyl sulfate (SIDS) polyacrylamide gels (7.5, 12.5, and 17.5%). Densitometric analysis of the Coomassie brilliant blue stained gels revealed alterations in the amounts of three protein bands in the exercised tissue relative to the control. These changes were in the linear portion of the graph of absorbance versus protein amount. Wilcoxon's signed rank test showed the first two of the following bands to increase significantly in amount (P < 0.062). The average percentage changes [mean (SEM)] for these bands were 63 (21), 39 (5), and 82 (35). The corresponding molecular weights determined from known standards were 76 300 (860), 33 200 (310), and 12 000 (80) daltons, respectively. These changes imply that the increased synthesis, decreased degradation, or some combination thereof, of these three proteins may be necessary for the repair or regeneration response to exercise-induced muscle damage.     

Muscle strength, volume and activation following 12-month resistance training in 70-year-old males

In elderly males muscle plantar flexor maximal voluntary contraction (MVC) torque normalised to muscle volume (MVC/VOL) is reduced compared to young males as a result of incomplete muscle activation in the elderly. The aim of the present study was to determine the influence of a 12-month resistance training programme on muscle volume, strength, MVC/VOL, agonist activation and antagonist coactivation of the plantarfexors in elderly males. Thirteen elderly males aged 70 years and over (range 70–82 years), completed a 12-month whole body resistance-training programme (TRN), training three times a week. Another eight males (range 18–30 years), who maintained their habitual physical activity for the same 12-month period as the TRN group acted as controls (CTRL). Isometric plantarflexor maximal voluntary contraction (MVC) torque increased in the TRN group by 20% (P<0.01), from 113.1±22.0 Nm to 141.5±19.2 Nm. Triceps surae volume (TS VOL) assessed using MRI, increased by 12%, from 796.3±78.9 cm³ to 916.8±144.4 cm³ . PF activation, measured using supramaximal double twitch interpolation, increased from 83.6±11.0% pre training, to 92.1±7.6% post training (P<0.05). Dorsiflexion MVC and antagonist coactivation (assessed using surface electromyography) did not change with training. Plantarflexor MVC torque normalized for triceps surae muscle volume (MVC/VOL) was 142.6±32.4 kN m^–2 before training and 157.0± 27.9 kN m^–2 after training (a non-significant increase of 8%). No significant change in any measurement was observed in the CTRL group. This study has shown that the gain in muscle strength in response to long-term (12-month) training in older men is mostly accounted for by an increased muscle volume and activation.     

Physiological hypertrophy of the FHL muscle following 8 weeks of progressive resistance exercise in the rat.

In humans, progressive resistance exercise is recognized for its ability to induce skeletal muscle hypertrophy. In an attempt to develop an animal model which mimics human progressive resistance exercise, Sprague-Dawley rats were trained to climb a 1.1-m vertical (80 degree incline) ladder with weights secured to their tail. The rats were trained once every 3 days for 8 weeks. Each training session consisted of 4-9 (6.02 +/- 0.23) climbs requiring 8-12 dynamic movements per climb. Based on performance, the weight carried during each session was progressively increased. Over the course of 8 weeks, the maximal amount of weight the rats could carry increased 287%, p 相似文献   

Effect of training on proteinuria following muscular exercise

Summary As a consequence of a short and exhaustive exercise, proteinuria increases due to haemoconcentration; proteins in urine increase from 40.4 ± 7.7 mg to mg 922.8 ± 19.1 and the A/G ratio in urine increases from 0.57 ± 0.01 to 1.54 ± 0.12, a value which is about the same as in plasma proteins.Exercise proteinuria seems to be independent from pH and from modifications of lactic acid serum level; it is probably due to secretion of l-noradrenaline during exercise, as infusion of this substance induces the same changes as exercise.After a 50 days' training, exercise proteinuria and proteinemia show a progressive decrease, while the inversion of urinary A/G ratio after exercise remains unaltered.     

Left atrial functional changes following short-term exercise training

Background

Exercise-induced adaptations of the human atria remain understudied, particularly early in the training process. We examined the effects of short-term high-intensity interval training (HIT) and continuous moderate-intensity training (CMT) on left atrial (LA) systolic and diastolic function, relative to left ventricular (LV) function in young, healthy men, by speckle tracking echocardiography (STE).

Methods

Fourteen untrained men (mean age = 25 ± 4 years) were randomized to HIT or CMT, and assessed before and after six training sessions over a 12-day period. HIT included 8-12 intervals of cycling for 60 s at 95–100 % of maximal aerobic power (VO_2MAX), interspersed by 75 s of cycling at 10 % VO_2MAX. CMT consisted of 90–120 min of cycling at 65 % VO_2MAX.

Results

VO_2MAX increased following HIT and CMT by 11.5 and 5.5 %, respectively (p < 0.05). Calculated plasma volume expanded 11 % following HIT and 10 % following CMT (p < 0.005). Resting LV volumes and ejection fraction were unaltered following training. Peak atrial longitudinal strain increased following HIT (41.8 ± 5.2 %–47.1 ± 3.7 %, p < 0.01) and CMT (38.5 ± 4.6 %–41.7 ± 6.0 %, p < 0.01). Atrial systolic strain rate increased following HIT (1.6 ± 0.2 %/s–2.0 ± 0.3 %/s, p < 0.01) and CMT (1.6 ± 0.2 %/s–1.9 ± 0.2 %/s, p < 0.01).

Conclusions

LA function assessed by STE improves rapidly during short-term intensive exercise training.     

Muscle strength and exercise intensity adaptation to resistance training in older women with knee osteoarthritis and total knee arthroplasty

OBJECTIVES:

To analyze muscle strength and exercise intensity adaptation to resistance training in older women with knee osteoarthritis and total knee arthroplasty.

METHODS:

Twenty-three community-dwelling women were divided into the following groups: older, with knee osteoarthritis and total knee arthroplasty in the contralateral limb (OKG; N = 7); older, without symptomatic osteoarthritis (OG; N = 8); and young and healthy (YG; N = 8). Muscle strength (1-repetition maximum strength test) and exercise intensity progression (workload increases of 5%–10% were made whenever adaptation occurred) were compared before and after 13 weeks of a twice-weekly progressive resistance-training program.

RESULTS:

At baseline, OKG subjects displayed lower muscle strength than those in both the OG and YG. Among OKG subjects, baseline muscle strength was lower in the osteoarthritic leg than in the total arthroplasty leg. Muscle strength improved significantly during follow-up in all groups; however, greater increases were observed in the osteoarthritic leg than in the total knee arthroplasty leg in OKG subjects. Greater increases were also seen in the osteoarthritic leg of OKG than in OG and YG. The greater muscle strength increase in the osteoarthritic leg reduced the interleg difference in muscle strength in OKG subjects, and resulted in similar posttraining muscle strength between OKG and OG in two of the three exercises analyzed. Greater exercise intensity progression was also observed in OKG subjects than in both OG and YG subjects.

CONCLUSIONS:

OKG subjects displayed greater relative muscle strength increases (osteoarthritic leg) than subjects in the YG, and greater relative exercise intensity progression than subjects in both OG and YG. These results suggest that resistance training is an effective method to counteract the lower-extremity strength deficits reported in older women with knee osteoarthritis and total knee arthroplasty.     

Performance and physiological responses to a 5-week synchronized swimming technical training programme in humans

A synchronized swimming team routine (TR) is composed of figures of varying degrees of difficulty. Swimmers able to perform these figures separately underwent a 5-week technical training programme (TTP) to assemble a TR. Little is known about the physiological responses to this kind of TTP. A group of 13 trained synchronized swimmers [mean age 14 (SD 1) years] were tested before and after a 5-week TTP. The TR lasted 5?min, and 45% of that time was spent underwater. The swimmers' technique scores in the TR improved significantly from 4.5 (SD 1.9) before to 5.8 (SD 2.3) points after the TTP (P?V˙O_2peak), blood lactate concentration, and heart rate measured during a 400-m swim were lower after the TTP. The improvement in the technique scores correlated negatively with the change in V˙O_2peak (r?=??0.57; P?V˙O_2peak. The overall synchronized swimming skill was assessed by the best score the swimmers obtained in four to six competitions over a season. This score was related to the 400-m swimming performance, V˙O_2peak, maximal distance covered in apnoea, and the breath-hold time. The 5-week TTP therefore improved technical performance during the TR without improving physiological, swimming or apnoea performances. However, the physiological profile of each swimmer was linked to the synchronized swimming skill.     

Hypotension following mild bouts of resistance exercise and submaximal dynamic exercise

Our purposes were (1) to examine resting arterial blood pressure following an acute bout of resistance exercise and submaximal dynamic exercise, (2) to examine the effects of these exercises on the plasma concentrations of atrial natriuretic peptide ([ANP]), and (3) to evaluate the potential relationship between [ANP] and post-exercise blood pressure. Thirteen males [24.3 ± (2.4) years] performed 15 min of unilateral leg press exercise (65% of their one-repetition maximum) and, 1 week later, ≈15 min of cycle ergometry (at 65% of their maximum oxygen consumption). Intra-arterial pressure was monitored during exercise and for 1 h post-exercise. Arterial blood was drawn at rest, during exercise and at intervals up to 60 min post-exercise for analysis of haematocrit and [αANP]. No differences occurred in blood pressure between trials, but significant decrements occurred following exercise in both trials. Systolic pressure was ≈20 mmHg lower than before exercise after 10 min, and mean pressure was ≈7 mmHg lower from 30 min onwards. Only slight (non-significant) elevations in [αANP] were detected immediately following exercise, with the concentrations declining to pre-exercise values by 5 min post-exercise. We conclude that post-exercise hypotension occurs following acute bouts of either resistance or submaximal dynamic exercise and, in this investigation, that this decreased blood pressure was not directly related to the release of αANP. Accepted: 29 July 1998