Inspiratory muscle function with restrictive chest wall loading during exercise in normal humans

The effects of selective restriction of rib cage (Res,rc) and abdominal wall (Res,ab) movements on endurance of short-term constant-load heavy exercise and on diaphragmatic function during such exercise were examined in five normal young men. An inelastic surgical corset was used to achieve Res,rc and Res,ab. Subjects exercised on a cycle ergometer at 80% of their maximum power output to exhaustion on three occasions: with Res,rc, with Res,ab, and without restriction of chest wall movements (control). Transdiaphragmatic (Pdi), esophageal, and gastric pressures were measured. Electromyogram of the diaphragm was recorded by an esophageal electrode, and the ratio of the power content of a high-frequency to low-frequency band (H/L ratio) was measured. In addition, maximum Pdi (Pdimax) pre- and immediately postexercise was recorded. Res,rc was associated with a shorter endurance time, a progressive decline of the H/L ratio, and a significant reduction of Pdimax postexercise, whereas no such changes were found with Res,ab. We conclude that diaphragmatic function was well defended with abdominal wall loading, whereas limitation of rib cage expansion reduced diaphragmatic endurance during exercise. The diaphragmatic tension-time index (TTdi) in exercise was always less than the critical value of 0.15 found by Bellemare and Grassino (J. Appl. Physiol. 53: 1190-1195, 1982) when subjects inspired against large resistive loads at normal minute ventilations. We suggest that the higher inspiratory flow rate (P less than 0.05) and breathing frequency (P less than 0.05) account for the occurrence of diaphragmatic fatigue in exercise with Res,rc when the TTdi was 0.06 +/- 0.02.     

Plasma renin system during exercise in normal men

The exercise-related increase in plasma renin activity (PRA) and in the plasma concentration of angiotensin II (ANG II) and aldosterone (Aldo) was studied in 43 healthy volunteers whose 24-h urinary sodium excretion (UVNa) ranged from 10 to 250 mmol. Arterial blood samples were obtained at rest and during bicycle ergometry. Compared with rest, PRA, ANG II, and Aldo rose to a similar extent during light and moderate exercise. However, at peak exercise ANG II increased significantly more (P less than 0.001) than PRA and Aldo. Thus, with increasing intensity of exercise, the slope of the linear regression of ANG II on PRA became significantly (P less than 0.001) steeper, whereas at maximal exercise the Aldo response did not follow the acute rise in ANG II. At rest as well as during exercise, Aldo rose with increasing ANG II, but the stimulatory effect of ANG II on Aldo was attenuated with higher sodium intake, as estimated from UVNa. Finally, independent of the level of physical activity, UVNa was negatively correlated with PRA, ANG II, and Aldo.     

Effects of low-intensity resistance exercise with slow movement and tonic force generation on muscular function in young men.

We investigated the acute and long-term effects of low-intensity resistance exercise (knee extension) with slow movement and tonic force generation on muscular size and strength. This type of exercise was expected to enhance the intramuscular hypoxic environment that might be a factor for muscular hypertrophy. Twenty-four healthy young men without experience of regular exercise training were assigned into three groups (n = 8 for each) and performed the following resistance exercise regimens: low-intensity [ approximately 50% of one-repetition maximum (1RM)] with slow movement and tonic force generation (3 s for eccentric and concentric actions, 1-s pause, and no relaxing phase; LST); high-intensity ( approximately 80% 1RM) with normal speed (1 s for concentric and eccentric actions, 1 s for relaxing; HN); low-intensity with normal speed (same intensity as for LST and same speed as for HN; LN). In LST and HN, the mean repetition maximum was 8RM. In LN, both intensity and amount of work were matched with those for LST. Each exercise session consisting of three sets was performed three times a week for 12 wk. In LST and HN, exercise training caused significant (P < 0.05) increases in cross-sectional area determined with MRI and isometric strength (maximal voluntary contraction) of the knee extensors, whereas no significant changes were seen in LN. Electromyographic and near-infrared spectroscopic analyses showed that one bout of LST causes sustained muscular activity and the largest muscle deoxygenation among the three types of exercise. The results suggest that intramuscular oxygen environment is important for exercise-induced muscular hypertrophy.     

Plasma insulin and C-peptide responses to oral glucose load after physical exercise in men with normal and impaired glucose tolerance

Blood glucose, plasma insulin and C-peptide responses to oral glucose tolerance test (OGTT) were studied under basal conditions and immediately after 90-min exercise (60% VO2 max) in nondiabetic subjects with normal or impaired glucose tolerance. During the postexercise recovery blood glucose response to OGTT was increased in normal subjects and markedly decreased in those with impaired glucose tolerance, while insulin and C-peptide responses were diminished in both subgroups. The ratio of blood glucose to insulin was similarly elevated in all subjects. Comparing with basal conditions no significant changes were found in C-peptide to insulin ratio in response to OGTT after exercise, although a tendency towards an elevation of this ratio was noted in the subjects with impaired glucose tolerance. The data indicate that the reduced insulin response to OGTT during postexercise recovery in healthy subjects is due to diminished insulin secretion without any substantial changes in the hormone removal from blood, whereas in the glucose intolerant men the latter process may be enhanced.     

Leukocytosis occurs in response to resistance exercise in men

The purpose of this study was to determine the effects of a single bout of resistance exercise on immune cell numbers of moderately active men. Subjects were 16 male volunteers (mean +/- standard deviation [SD] age 30 +/- 7 years, height 180.1 +/- 7.0 cm, mass 83.97 +/- 10.33 kg); 8 were randomly assigned to treatment and 8 to control groups. Treatment was a common resistance training routine (3 sets of 8-10 repetitions at 75% of 1 repetition maximum) of 8 large muscle mass exercises using resistance machines. Blood samples were drawn before exercise and at 0 minutes (P0), 15 minutes (P15), and 30 minutes (P30) postexercise. Control subjects sat quietly in the training facility; blood was drawn at the same intervals as treatment. Leukocyte and lymphocyte (LY) subpopulation numbers were determined. Statistical analysis was analysis of variance (ANOVA) (repeated measures, p < or = 0.050) and multiple comparisons (Dunn method) to isolate variability. All leukocyte subpopulations, except basophils (BA) and eosinophils (EO), increased and counts declined by P15 and P30. Only neutrophils (NE) did not return to preexercise levels by P30. The majority of resistance exercise induced leukocytosis was due to an increase in circulating LY (natural killer cells increased most, CD4+/CD8+ ratio unchanged) and monocytes (MO). The transient, inconsequential immune cell population responses to resistance exercise are similar to those during aerobic activity. The lack of large alterations in and rapid recovery from cell number changes suggests that resistance exercise is not immunosuppressive.     

Fat metabolism and acute resistance exercise in trained men.

The purpose of this study was to investigate the effect of acute resistance exercise (RE) on lipolysis within adipose tissue and subsequent substrate oxidation to better understand how RE may contribute to improvements in body composition. Lipolysis and blood flow were measured in abdominal subcutaneous adipose tissue via microdialysis before, during, and for 5 h following whole body RE as well as on a nonexercise control day (C) in eight young (24 +/- 0.7 yr), active (>3 RE session/wk for at least 2 yr) male participants. Fat oxidation was measured immediately before and after RE via indirect calorimetry for 45 min. Dialysate glycerol concentration (an index of lipolysis) was higher during (RE: 200.4 +/- 38.6 vs. C: 112.4 +/- 13.1 micromol/l, 78% difference; P = 0.02) and immediately following RE (RE: 184 +/- 41 vs. C: 105 + 14.6 micromol/l, 75% difference; P = 0.03) compared with the same time period on the C day. Energy expenditure was elevated in the 45 min after RE compared with the same time period on the C day (RE: 104.4 +/- 6.0 vs. C: 94.5 +/- 4.0 kcal/h, 10.5% difference; P = 0.03). Respiratory exchange ratio was lower (RE: 0.71 +/- 0.004 vs. C: 0.85 +/- .03, 16.5% difference; P = 0.004) and fat oxidation was higher (RE: 10.2 +/- 0.8 vs. C: 5.0 +/- 1.0 g/h, 105% difference; P = 0.004) following RE compared with the same time period on the C day. Therefore, the mechanism behind RE contributing to improved body composition is in part due to enhanced abdominal subcutaneous adipose tissue lipolysis and improved whole body fat oxidation and energy expenditure in response to RE.     

Androgen receptor content following heavy resistance exercise in men

The purpose of the present investigation was to examine androgen receptor (AR) content in the vastus lateralis following two resistance exercise protocols of different volume. Nine resistance-trained men (age=24.3+/-4.4 years) performed the squat exercise for 1 (SS) and 6 sets (MS) of 10 repetitions in a random, counter-balanced order. Muscle biopsies were performed at baseline, and 1h following each protocol. Blood was collected prior to, immediately following (IP), and every 15 min after each protocol for 1h. No acute elevations in serum total testosterone were observed following SS, whereas significant 16-23% elevations were observed at IP, 15, and 30 min post-exercise following MS. No acute elevations in plasma cortisol were observed following SS, whereas significant 31-49% elevations were observed for MS at IP, 15, and 30 min post-exercise. Androgen receptor content did not change 1h following SS but significantly decreased by 46% following MS. These results demonstrated that a higher volume of resistance exercise resulted in down-regulation of AR content 1h post-exercise. This may have been due to greater protein catabolism associated with the higher level of stress following higher-volume resistance exercise.     

Pro-antioxidant ratio in healthy men exposed to muscle-damaging resistance exercise

The purpose of this study was to compare the pro-antioxidant status in healthy men exposed to muscle-damaging resistance exercise, and to investigate the practical application of Loverro's coefficient (P/A ratio) to evaluate the presence of oxidative stress. Twenty-eight healthy men were assigned to two groups performed multi-joint (M) or single-joint (S) resistance exercise. The activities of superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) as well as the concentration of lipid peroxidation products (TBARS) in blood were evaluated. The P/A ratio was calculated from the mean values of erythrocyte TBARS, SOD, CAT and GPx. Creatine kinase (CK) activity was used as a marker of muscle damage. The applied resistance exercises triggered off the changes in pro-antioxidant ratio towards peroxidation which was proved by significant increase in erythrocyte TBARS concentration in M (+25%) and S (+27%) groups. Plasma TBARS increased only after multi-joint resistance exercise and correlated with erythrocyte P/A ratio (r = 0.536, P < 0.01). The multi-joint exercise caused decrease in SOD activity by 28% whereas the single-joint resistance exercise elevated enzyme activity by 20%. Activities of the other antioxidant enzymes changed simultaneously i.e. CAT activity increased by 14%-16% immediately after exercise, and GPx activity declined by 18%-34% during recovery in M and S groups. Even though, all erythrocyte parameters significantly changed following multi-joint and single-joint resistance exercises, the assessment of pro-antioxidant ratio showed the considerable increase in P/A only in M group. In summary, an analysis of pro- and antioxidant parameters showed significant changes in response to muscle-damaging exercise and demonstrated the practical application of P/A ratio to evaluate the risk of oxidative stress in athletes.     

Myofibrillar disruption following acute concentric and eccentric resistance exercise in strength-trained men

We have previously quantified the extent of myofibrillar disruption which occurs following an acute bout of resistance exercise in untrained men, however the response of well-trained subjects is not known. We therefore recruited six strength-trained men, who ceased training for 5 days and then performed 8 sets of 8 uni-lateral repetitions, using a load equivalent to 80% of their concentric (Con) 1-repetition maximum. One arm performed only Con actions by lifting the weight and the other arm performed only eccentric actions (Ecc) by lowering it. Needle biopsy samples were obtained from biceps brachii of each arm approximately 21 h following exercise, and at baseline (i.e., after 5 days without training), and subsequently analyzed using electron microscopy to quantify myofibrillar disruption. A greater (P < or = 0.05) proportion of disrupted fibres was found in the Ecc arm (45 +/- 11%) compared with baseline values (4 +/- 2%), whereas fibre disruption in the Con arm (27 +/- 4%) was not different (P > 0.05) from baseline values. The proportion of disrupted fibres and the magnitude of disruption (quantified by sarcomere counting) was considerably less severe than previously observed in untrained subjects after an identical exercise bout. Mixed muscle protein synthesis, assessed from approximately 21-29 h post-exercise, was not different between the Con- and Ecc-exercised arms. We conclude that the Ecc phase of resistance exercise is most disruptive to skeletal muscle and that training attenuates the severity of this effect. Moreover, it appears that fibre disruption induced by habitual weightlifting exercise is essentially repaired after 5 days of inactivity in trained men.     

Acute hormonal responses to heavy resistance exercise in younger and older men

The purpose of this investigation was to examine the acute responses of several hormones [total and free testosterone (TT and FT, respectively), adrenocorticotropic hormone (ACTH), cortisol (C), growth hormone (GH), and insulin (INS)] to a single bout of heavy resistance exercise (HRE). Eight younger [30-year (30y) group] and nine older [62-year (62y) group] men matched for general physical characteristics and activity levels performed four sets of ten repetitions maximum (RM) squats with 90 s rest between sets. Blood samples were obtained from each subject via an indwelling cannula with a saline lock pre-exercise, immediately post-exercise (IP), and 5, 15 and 30 min post-exercise. Levels of TT, FT, ACTH, C and lactate significantly increased after HRE for both groups. Pre-HRE pairwise differences between groups were noted only for FT, while post-HRE pairwise differences were found for TT, FT, GH, glucose and lactate. Area under the curve analysis showed that the 30y group had a significantly higher magnitude of increase over the entire recovery period (IP, 5, 15, and 30 min post-exercise) for TT, FT, ACTH and GH. Few changes occurred in the INS response with the only change being that the 62y group demonstrated a decrease IP. Lactate remained elevated at 30 min post-HRE. This investigation demonstrates that age-related differences occur in the endocrine response to HRE, and the most striking changes appear evident in the FT response to HRE in physically active young and older men. Accepted: 11 June 1997     

Hormonal responses to resistance exercise in long-term trained and untrained middle-aged men

This cross-sectional study compared hormonal responses to resistance exercise between trained and untrained men to investigate the adaptations of the endocrine system to long-term strength training in middle-aged men. Twenty-one middle-aged men were recruited for this study and matched into a strength-trained group (SG) (n = 10) and an untrained group (UG) (n = 11). In the SG, the individuals had practiced strength training for hypertrophy for at least 3 years. Upper- and lower-body muscle strength was measured with a 1 repetition maximum (1RM) test. Blood samples were collected at rest and after multiple sets of a superset strength training protocol (SSTP), with an intensity of 75% of 1RM values. With these blood samples, the levels of total testosterone (TT), free testosterone (FT), dehydroepiandrosterone (DHEA), cortisol, and sex hormone-binding globulin (SHBG) were determined. In addition, the TT-to-cortisol ratio and TT-to-SHBG ratio were calculated. There was no difference at rest between groups in hormonal values for TT, FT, DHEA, cortisol, the TT-to-SHBG ratio, and the TT-to-cortisol ratio. There were increases after SSTP in the levels of TT, FT, DHEA, and cortisol and the TT-to-SHBG ratio in the UG, but only FT increased in the SG. The SG demonstrated lower values in the TT-to-SHBG ratio after the training session. These results suggest the presence of alterations in anabolic and catabolic hormonal responses to resistance exercise in long-term trained middle-aged men, with the trained subjects demonstrating lower responsiveness in the hormone values. Long-term trained men seem to require a higher volume of training, at least similar to their daily workout, to stimulate greater hormone responses.     

Plasma catecholamine responses to four resistance exercise tests in men and women

The plasma adrenaline ([A]) and noradrenaline ([NA]) concentration responses of nine men and eight women were investigated in four resistance exercise tests (E80, E60, E40 and E20), in which the subjects had to perform a maximal number of bilateral knee extension-flexion movements at a given cycle pace of 0.5 Hz, but at different load levels (80%, 60%, 40% and 20% of 1 repetition maximum, respectively). The four test sessions were separated by a minimal interval of 3 rest days. The number of repetitions (Repmax), the total work (Wtot) done normalized for the lean body mass and the heart rate (HR) responses were similar in the two groups in each test. In addition, no differences were found between the two groups in [A] and [NA] either before or after the exercise tests. The postexercise [NA], both in the men [10.8 (SD 7.0) nmol x l(-1)] and in the women [11.7 (SD 7.4) nmol x l(-1)], was clearly the highest in E20, where also the Repmax, WtOt, the total amount of integrated electromyograph activity in the agonist muscles and the peak postexercise blood lactate concentration [men 8.3 (SD 1.6) vs women 7.3 (SD 0.9) mmol x l(-1), ns] were significantly higher than in the other tests. Although the postexercise [A] in E20 both in the men [7.1 (SD 6.0) nmol x l(-1)] and in the women [5.2 (SD 2.0) nmol x l(-1)] were higher than in E80 [men 3.1 (SD 4.2), women 2.1 (SD 2.0) nmol x l(-l)] (P < 0.05), they were not significantly different from E60 [men 3.6 (SD 1.9), women 4.0 (SD 3.3) nmol x l(-1)] and E40 [men 3.8 (SD 4.1), women 5.8 (SD 4.0) nmol x l(-1)] in either group. The present study did not indicate any sex differences in performance and in plasma catecholamine responses in different exhausting resistance exercise tests performed with the knee extensor muscles. In both groups the plasma [NA] response was clearly the largest in the longest exercise with the greatest amount of muscle activity and work done, and with the largest blood lactate response. The differences in the plasma [A] responses between the exercises tended to be somewhat smaller.