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.     

Acute testosterone and cortisol responses to high power resistance exercise

This study examined the acute hormonal responses to a single high power resistance exercise training session. Four weight trained men (X ± SD; age [yrs] = 24.5 ± 2.9; hgt [m] = 1.82 ± 0.05; BW [kg] = 96.9 ± 10.6; 1 RM barbell squat [kg] = 129.3 ± 17.4) participated as subjects in two randomly ordered sessions. During the lifting session, serum samples were collected pre- and 5 min post-exercise, and later analyzed for testosterone (Tes), cortisol (Cort), their ratio (Tes/Cort), and lactate (HLa). The lifting protocol was 10 × 5 speed squats at 70% of system mass (1 RM + BW) with 2 min inter-set rest intervals. Mean power and velocity were determined for each repetition using an external dynamometer. On the control day, the procedures and times (1600–1900 h) were identical except the subjects did not lift. Tes and Cort were analyzed via EIA. Mean ± SD power and velocity was 1377.1 ± 9.6 W and 0.79 ± 0.01 m s⁻¹ respectively for all repetitions, and did not decrease over the 10 sets (p < 0.05). Although not significant, post-exercise Tes exhibited a very large effect size (nmol L⁻¹; pre = 12.5 ± 2.9, post = 20.0 ± 3.9; Cohen’s D = 1.27). No changes were observed for either Cort or the Tes/Cort ratio. HLa significantly increased post-exercise (mmol L⁻¹; pre = 1.00 ± 0.09, post = 4.85 ± 1.10). The exercise protocol resulted in no significant changes in Tes, Cort or the Tes/Cort ratio, although the Cohen’s D value indicates a very large effect size for the Tes response. The acute increase for Tes is in agreement with previous reports that high power activities can elicit a Tes response. High power resistance exercise protocols such as the one used in the present study produce acute increases of Tes. These results indicate that high power resistance exercise can contribute to an anabolic hormonal response with this type of training, and may partially explain the muscle hypertrophy observed in athletes who routinely employ high power resistance exercise.     

Work volume and strength training responses to resistive exercise improve with periodic heat extraction from the palm

Body core cooling via the palm of a hand increases work volume during resistive exercise. We asked: (a) "Is there a correlation between elevated core temperatures and fatigue onset during resistive exercise?" and (b) "Does palm cooling between sets of resistive exercise affect strength and work volume training responses?" Core temperature was manipulated by 30-45 minutes of fixed load and duration treadmill exercise in the heat with or without palm cooling. Work volume was then assessed by 4 sets of fixed load bench press exercises. Core temperatures were reduced and work volumes increased after palm cooling (Control: Tes = 39.0 ± 0.1° C, 36 ± 7 reps vs. Cooling: Tes = 38.4 ± 0.2° C, 42 ± 7 reps, mean ± SD, n = 8, p < 0.001). In separate experiments, the impact of palm cooling on work volume and strength training responses were assessed. The participants completed biweekly bench press or pull-up exercises for multiple successive weeks. Palm cooling was applied for 3 minutes between sets of exercise. Over 3 weeks of bench press training, palm cooling increased work volume by 40% (vs. 13% with no treatment; n = 8, p < 0.05). Over 6 weeks of pull-up training, palm cooling increased work volume by 144% in pull-up experienced subjects (vs. 5% over 2 weeks with no treatment; n = 7, p < 0.001) and by 80% in pull-up na?ve subjects (vs. 20% with no treatment; n = 11, p < 0.01). Strength (1 repetition maximum) increased 22% over 10 weeks of pyramid bench press training (4 weeks with no treatment followed by 6 weeks with palm cooling; n = 10, p < 0.001). These results verify previous observations about the effects of palm cooling on work volume, demonstrate a link between core temperature and fatigue onset during resistive exercise, and suggest a novel means for improving strength and work volume training responses.     

Effect of repeated bouts of short-term exercise on plasma free and sulphoconjugated catecholamines in humans

We tested the hypothesis that measurement of plasma catecholamine sulphate concentration after exercise reflects the overall activation of the sympathoadrenergic system during the whole period of repeated bouts of short-term exercise. A group of 11 male athletes performed two exercise tests at similar average power outputs consisting of three sets each. The tests either started with one set of three very intense sprints (95% of maximal running speed) followed by two sets of three less intense sprints (85% of maximal running speed; HLX) or vice versa (LHX). Similar mean areas under the curve of free noradrenaline (NA) during HLX and LHX [622 (SEM 13) v.s. 611 (SEM 14) nmol x l(-1) min) as well as similar mean heart rates [143 (SEM 9) v.s. 143 (SEM 8) beats x min(-1)] indicated comparable sympathetic activation during both exercise tests. Even so, plasma concentration of free NA was still significantly higher at the end of LHX than of HLX [35.7 (SEM 3.5) v.s. 22.5 (SEM 2.1) nmol x l(-1), respectively], i.e. when exercise ended with the more intense set of sprints. Plasma noradrenaline sulphate (NA-S) increased with exercise intensity showing higher mean increments after the first set of HLX compared to LHX [1.83 (SEM 0.42) v.s. 1.18 (SEM 0.29) nmol x l(-1); P<0.05]. However, after the end of HLX and LHX, increments in plasma NA-S were similar [4.52 (SEM 0.76) v.s. 4.06 (SEM 0.79) nmol x l(-1)], suggesting that NA-S response changed in parallel with the overall activation of the sympathetic nervous system during repeated bouts of short-term exercise. The results supported the hypothesis that measurement of plasma NA-S immediately after repeated bouts of short-term exercise reflects overall activation of the sympathetic nervous system during prolonged periods of this type of exercise.     

Effects of low-intensity resistance exercise under acute systemic hypoxia on hormonal responses

Previous studies have shown that low-intensity resistance exercises with vascular occlusion and slow movement effectively increase muscular size and strength. Researchers have speculated that local hypoxia by occlusion and slow movement may contribute to such adaptations via promoting anabolic hormone secretions by the local accumulation of metabolites. In this study, we determined the effects of low-intensity resistance exercise under acute systemic hypoxia on metabolic and hormonal responses. Eight male subjects participated in 2 experimental trials: (a) low-intensity resistance exercise while breathing normoxic air (normoxic resistance exercise [NR]), (b) low-intensity resistance exercise while breathing 13% oxygen (hypoxic resistance exercise [HR]). The resistance exercises (bench press and leg press) consisted of 14 repetitions for 5 sets at 50% of maximum strength with 1 minute of rest between sets. Blood lactate (LA), serum growth hormone (GH), norepinephrine (NE), testosterone, and cortisol concentrations were measured before normoxia and hypoxia exposures; 15 minutes after the exposures; and at 0, 15, and 30 minutes after the exercises. The LA levels significantly increased after exercises in both trials (p ≤ 0.05). The area under the curve for LA after exercises was significantly higher in the HR trial than in the NR trial (p ≤ 0.05). The GH significantly increased only after the HR trial (p ≤ 0.05). The NE and testosterone significantly increased after the exercises in both trials (p ≤ 0.05). Cortisol did not significantly change in both trials. These results suggest that low-intensity resistance exercise in the hypoxic condition caused greater metabolic and hormonal responses than that in the normoxic condition. Coaches may consider low-intensity resistance exercise under systemic hypoxia as a potential training method for athletes who need to maintain muscle mass and strength during the long in-season.     

Hormonal responses to a resistance exercise performed under the influence of delayed onset muscle soreness

Hormonal responses to an unaccustomed knee-extension exercise (E1; 5 times 10 repetitions with 40% load of 1RM [1 repetition maximum] followed by 2 sets until exhaustion) were compared in 6 men with the corresponding responses to an identical exercise performed 2 days later under the influence of delayed onset muscle soreness (DOMS) (E2). Both exercises were performed with a variable-resistance machine causing exhaustion with significantly fewer repetitions than a normal constant-resistance knee-extension device does. The E1 induced DOMS as expected, but the 1RM, the total work done, and the repetition number and frequency were not different in the 2 exercises. In the 2 sets to failure, the mean repetition number varied between 17 and 25. The exercise-induced norepinephrine, epinephrine, testosterone, cortisol (COR), and growth hormone (GH) increases were similar in the 2 exercises, although the overall level of COR and GH, including the preexercise concentrations, tended to decline in the second exercise. The results may thus suggest that the hormonal response to resistance exercise is not significantly altered when performed soon after an unaccustomed exercise bout leading to DOMS.     

Adrenergic response to intense muscular activity in sedentary subjects as a function of emotivity and training]

Seven male sedentary human subjects were studied during intense muscular work (80% of maximal oxygen uptake) performed either for 15 min or until exhaustion (mean duration: 47 +/- 2 min). Plasma catecholamines were estimated before and after the experiment by means of an original fluorimetric assay. Epinephrine or norepinephrine were individually isolated from plasma and assayed in single extracts by a highly sensitive fluorimetric method. Epinephrine and norepinephrine levels as low as 15 ng per liter were detectable by this procedure in human plasma. The adrenergic pattern was found to be greatly different from one subject to another and related to emotivity: the effect of this factor was revealed by the predominance of epinephrine in plasma at rest or under exercise (ratio NA/A less than 1). In nonemotive subjects (ratio NA/A greater than 1 at rest) plasma epinephrine and norepinephrine increased progressively during exercise. Increments after exercise were higher for norepinephrine changes; however, the fact that epinephrine concentrations correlated significantly with norepinephrine suggests a simulataneous and coordinated stimulation of adrenal glands and orthosympathetic nervous system. In emotive subjects (ratio NA/A less than 1 at rest) the apprehension of muscular work promoted a difference in catecholamine responses: norepinephrine release was not affected by subject's anxiety, while epinephrine secretion, already elevated before the test, reached a high degree of magnitude in the first minutes of muscular work, remaining nearly constant until exhaustion. Physical training of nonemotive subjects, during 2 months with two intense exercises by a week, reduced strongly norepinephrine release after exhaustive muscular work. In the same conditions, the adrenal-medullary response was not significantly modified when compared with untrained subjects. Our results suggest that the adrenergic behaviour during exercise is a function of effort intensity to be supplied; catecholamines seem to be important factors in regulating body homeostasy during muscular work in man. In addition, emotive subjects exhibit amplified adrenal-medullary response, which may be related to psychological stimuli.     

Plasma glucagon and catecholamines during exhaustive short-term exercise

Plasma glucagon and catecholamine levels were measured in male athletes before and after exhaustive 15 min continuous running and strenuous intermittent short-term exercise (3 X 300 m). Blood lactate levels were higher after the intermittent exercise (mean 16.7 mmol X 1(-1)) than after the continuous running (mean 7.1 mmol X 1(-1)). Plasma glucagon concentration increased during continuous running and intermittent exercise by 41% and 55%, respectively, and the increases in plasma noradrenaline concentration were 7.7- and 9.1-fold compared with the respective pre-exercise values. Immediately after the exercises plasma cyclic AMP, blood glucose and alanine levels were elevated significantly. The data suggest that the sympathoadrenal system is of major importance for liver glucose production during high-intensity exercises. Catecholamines directly stimulate liver glucose production and may indirectly stimulate it by enhancing the secretion of glucagon.     

Kinetics of heart rate and catecholamines during exercise in humans The effect of heart denervation

To elucidate the role of factors other than the nervous system in heart rate (f _c) control during exercise, the kinetics off _c and plasma catecholamine concentrations were studied in ten heart transplant recipients during and after 10-min cycle ergometer exercise at 50 W. Thef _c did not increase at the beginning of the exercise for about 60 s. Then in the eight subjects who completed the exercise it increased following an exponential kinetic with a mean time constant of 210 (SEM 22) s. The two other subjects were exhausted after 5 and 8 min of exercise during whichf _c increased linearly. At the cessation of the exercise,f _c remained unchanged for about 50 s and then decreased exponentially with a time constant which was unchanged from that at the beginning of exercise. In the group of eight subjects plasma noradrenaline concentration ([NA]) increased after 30 s to a mean value above resting of 547 (SEM 124) pg · ml^–1, showing a tendency to a plateau, while adrenaline concentration ([A]) did not increase significantly. In the two subjects who became exhausted an almost linear increase in [NA] occurred up to about 1,300 pg · ml^–1 coupled with a significant increase in [A]. During recovery an immediate decrease in [NA] was observed towards resting values. The values of thef _c increase above resting levels determined at the time of blood collection were linearly related with [NA] increments both at the beginning and end of exercise with a similar slope, i.e. about 2.5 beats · min^–1 per 100 pg · ml^–1 of [NA] change. These findings would seem to suggest that in the absence of heart innervation the increase inf _c depends on plasma [NA].     

Effects of unilateral and bilateral lower-body heavy resistance exercise on muscle activity and testosterone responses

Unilateral and bilateral lower-body heavy resistance exercises (HREs) are used for strength training. Little research has examined whether muscle activation and testosterone (TES) responses differ between these exercises. Our purpose was to compare the effects of unilateral and bilateral lower-body HRE on muscle activity using surface electromyography (sEMG) and TES concentrations. Ten resistance-trained, college-aged male athletes (football, track and field) completed 5 testing sessions in which bilateral (back squat [BS]) and unilateral (pitcher squat [PS]) exercises were performed using a counterbalanced design. Sessions 1 and 2 determined estimated maximum strength (10 repetition maximum [10RM]) in the BS and PS. During testing session 3, muscle activation (sEMG) was measured in the right vastus lateralis, biceps femoris, gluteus maximus, and erector spinae (ES) during both BS and PS (stance leg) exercises. In sessions 4 and 5, total TES concentrations (nanomoles per liter) were measured via blood draws at baseline (preexercise), 0, 5, 10, 15, and 30 minutes postexercise after 4 sets of 10 repetitions at the 10RM. Separate repeated-measures analyses of variance examined differences in sEMG and TES between BS and PS (p < 0.05). The sEMG amplitudes were similar (p = 0.80) for BS (0.22 ± 0.06 mV) and PS (0.20 ± 0.07 mV). The TES responses were also similar (p = 0.15) between BS (21.8 ± 6.9 nmol·L(-1)) and PS (26.2 ± 10.1 nmol·L(-1)). The similar lower limb and back sEMG and TES responses may indicate that the neuromuscular and hormonal demands were comparable for both the BS and PS exercises despite the absolute work being less in the PS. The PS exercise may be an effective method for including unilateral exercise into lower-body resistance training when designing training programs for ground-based activities.     

Heart rate and plasma catecholamines during 24 h of everyday life in trained and untrained men.

Physical training decreases resting heart rate as well as heart rate and catecholamine responses to ordinary physical activity and mental stress. These effects have been speculated to diminish cardiac morbidity. However, the sparing of heartbeats and catecholamine production might be outweighed by exaggerated responses during training sessions. To elucidate this issue, heart rate was measured continuously and plasma catecholamine concentrations were measured frequently during 24 h of ordinary living conditions in seven endurance-trained athletes (T) and eight sedentary or untrained (UT) young males. T subjects had lower heart rates than UT subjects during sleep and during nontraining awake periods. However, because of the increase during training, the total 24-h heartbeat number did not differ between groups (107,737 +/- 3,819 for T vs. 113,249 +/- 6,879 for UT, P = 0.731). Neither during sleep nor during awake nontraining periods were catecholamine levels lower in T than in UT subjects. Peak catecholamine levels during exercise in T were much higher than peak levels in UT subjects, and 24-h average epinephrine and norepinephrine concentrations were twice as high. We concluded that in highly trained athletes the total number of heartbeats per day is not decreased and the catecholamine production is, in fact, increased.     

Effect of two different rest period lengths on the number of repetitions performed during resistance training

The purpose of this study was to compare the effects of 2 different rest period lengths during a resistance training session with the number of repetitions completed per set of each exercise, the volume completed over 3 sets of each exercise, and the total volume during a training session. Fourteen experienced, weight-trained men volunteered to participate in the study. All subjects completed 2 experimental training sessions. Both sessions consisted of 3 sets of 8 repetitions with an 8 repetition maximum resistance of 6 upper body exercises performed in a set manner (wide grip lat pull-down, close grip pull-down, machine seated row, barbell row lying on a bench, dumbbell seated arm curl, and machine seated arm curl). The 2 experimental sessions differed only in the length of the rest period between sets and exercises: 1 session with a 1-minute and the other with a 3-minute rest period. For all exercises, results demonstrate a significantly lower total number of repetitions for all 3 sets of an exercise when 1-minute rest periods were used (p < or = 0.05). The 3- and 1-minute protocols both resulted in a significant decrease from set 1 to set 3 in 4 of the 6 exercises (p < or = 0.05), whereas the 1-minute protocol also demonstrated a significant decrease from set 1 to set 2 in 2 of the 6 exercises (p < or = 0.05). The results indicate that, during a resistance training session composed of all upper body exercises, 1-minute rest periods result in a decrease in the total number of repetitions performed compared with 3-minute rest periods between sets and exercises.     

Moderate resistance training volume produces more favorable strength gains than high or low volumes during a short-term training cycle

The purpose of this study was to examine the effects of 3 resistance training volumes on maximal strength in the snatch (Sn), clean & jerk (C&J), and squat (Sq) exercises during a 10-week training period. Fifty-one experienced (>3 years), trained junior lifters were randomly assigned to one of 3 groups: a low-volume group (LVG, n = 16), a moderate-volume group (MVG, n = 17), and a high-volume group (HVG, n = 18). All subjects trained 4-5 days a week with a periodized routine using the same exercises and relative intensities but a different total number of sets and repetitions at each relative load: LVG (1,923 repetitions), MVG (2,481 repetitions), and HVG (3,030 repetitions). The training was periodized from moderate intensity (60- 80% of 1 repetition maximum [1RM]) and high number of repetitions per set (2-6) to high intensity (90-100% of 1RM) and low number of repetitions per set (1-3). During the training period, the MVG showed a significant increase for the Sn, C&J, and Sq exercises (6.1, 3.7, and 4.2%, respectively, p < 0.01), whereas in the LVG and HVG, the increase took place only with the C&J exercise (3.7 and 3%, respectively, p < 0.05) and the Sq exercise (4.6%, p < 0.05, and 4.8%, p < 0.01, respectively). The increase in the Sn exercise for the MVG was significantly higher than in the LVG (p = 0.015). Calculation of effect sizes showed higher strength gains in the MVG than in the HVG or LVG. There were no significant differences between the LVG and HVG training volume-induced strength gains. The present results indicate that junior experienced lifters can optimize performance by exercising with only 85% or less of the maximal volume that they can tolerate. These observations may have important practical relevance for the optimal design of strength training programs for resistance-trained athletes, since we have shown that performing at a moderate volume is more effective and efficient than performing at a higher volume.     

Effects of 3-day bed rest on physiological responses to graded exercise in athletes and sedentary men.

To test the hypotheses that short-term bed-rest (BR) deconditioning influences metabolic, cardiorespiratory, and neurohormonal responses to exercise and that these effects depend on the subjects' training status, 12 sedentary men and 10 endurance- and 10 strength-trained athletes were submitted to 3-day BR. Before and after BR they performed incremental exercise test until volitional exhaustion. Respiratory gas exchange and heart rate (HR) were recorded continuously, and stroke volume (SV) was measured at submaximal loads. Blood was taken for lactate concentration ([LA]), epinephrine concentration ([Epi]), norepinephrine concentration ([NE]), plasma renin activity (PRA), human growth hormone concentration ([hGH]), testosterone, and cortisol determination. Reduction of peak oxygen uptake (VO(2 peak)) after BR was greater in the endurance athletes than in the remaining groups (17 vs. 10%). Decrements in VO(2 peak) correlated positively with the initial values (r = 0.73, P < 0.001). Resting and exercise respiratory exchange ratios were increased in athletes. Cardiac output was unchanged by BR in all groups, but exercise HR was increased and SV diminished in the sedentary subjects. The submaximal [LA] and [LA] thresholds were decreased in the endurance athletes from 71 to 60% VO(2 peak) (P < 0.001); they also had an earlier increase in [NE], an attenuated increase in [hGH], and accentuated PRA and cortisol elevations during exercise. These effects were insignificant in the remaining subjects. In conclusion, reduction of exercise performance and modifications in neurohormonal response to exercise after BR depend on the previous level and mode of physical training, being the most pronounced in the endurance athletes.     

Effect of exercise hemoconcentration and hyperosmolality on exercise responses

We investigated the effects of a decrease in plasma volume (PV) and an increase in plasma osmolality during exercise on circulatory and thermoregulatory responses. Six subjects cycled at approximately 65% of their maximum O2 uptake in a warm environment (30 degrees C, 40% relative humidity). After 30 min of control (C) exercise (no infusion), PV decreased 13.0%, or 419 +/- 106 (SD) ml, heart rate (HR) increased to 167 +/- 3 beats/min, and esophageal temperature (Tes) rose to 38.19 +/- 0.09 degrees C (SE). During infusion studies (INF), infusates were started after 10 min of exercise. The infusates contained 5% albumin suspended in 0.45, 0.9, or 3.0% saline. The volume of each infusate was adjusted so that during the last 10 min of exercise PV was maintained at the preexercise level and osmolality was allowed to differ. HR was significantly lower (10-16 beats/min) during INF than during C. Tes was reduced significantly during INF, with trends for increased skin blood flow and decreased sweating rates. No significant differences in HR, Tes, or sweating rate occurred between the three infusion conditions. We conclude that the decrease in PV, which normally accompanies moderate cycle exercise, compromises circulatory and thermal regulations. Increases in osmolality appear to have small if any effects during such short-term exercise.     

Beta-endorphin, adrenocorticotropic hormone, cortisol and catecholamines during aerobic and anaerobic exercise

Twelve non-specifically trained volunteers (aged 26.5 years, SD 3.6) performed exhausting incremental graded exercise (ST) and 1-min anaerobic cycle ergometer exercise (AnT) at 2-h intervals for the purpose of investigating beta-endorphin (beta-E) behaviour dependent on exercise intensity and anaerobic metabolism. In order to determine [beta-E], adrenocorticotropic hormone [ACTH], cortisol [C], adrenaline [A] and noradrenaline [NA] concentrations, venous blood samples were collected prior and subsequent to exercise until the 20th min of the recovery period, as well as in ST before and after exceeding the individual anaerobic threshold (THan,i). Before, during and after ST, lactate concentration, heart rate and perceived degree of exertion were also determined; after AnT maximum lactate concentration was measured. Both types of exercise led to significant increases in [beta-E], [ACTH], [A] and [NA], with levels of [beta-E] and [ACTH] approximately twice as high after ST as after AnT. The [C] increased significantly only after ST. During ST significant changes in [beta-E] and [ACTH] were measured only after exceeding THan,i. At all measuring times before and after ST and AnT both hormones correlated positively. In AnT the increases of [beta-E] and [A] demonstrated a correlation (r = 0.65; P less than 0.05). Both in AnT and ST there was a relationship between the maximum concentrations of beta-E and lactate (r = 0.63 and 0.71; each P less than 0.05). We therefore conclude that physical exercise with increasing or mostly anaerobic components leads to an increase in [beta-E], the extent correlating with the degree of lactate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute effects of plyometric exercise on maximum squat performance in male athletes

This study examines the acute effects of plyometric exercise on 1 repetition maximum (RM) squat performance in trained male athletes. Twelve men (mean age +/- SD: 20.5 +/- 1.4 years) volunteered to participate in 3 testing sessions separated by at least 6 days of rest. During each testing session the 1RM was assessed on back squat exercise. Before all 3 trials subjects warmed up on a stationary cycle for 5 minutes and performed static stretching. Subjects then performed 5 submaximal sets of 1-8 repetitions before attempting a 1RM lift. Subjects rested for at least 4 minutes between 1RM trials. During the first testing session (T1) subjects performed a series of sets with increasing load until their 1RM was determined. During the second and third testing sessions subjects performed in counterbalanced order either 3 double-leg tuck jumps (TJ) or 2 depth jumps (DJ) 30 seconds before each 1RM attempt. The average 1RM lifts after T1 and testing sessions with TJ or DJ were 139.6 +/- 29.3 kg, 140.5 +/- 25.6 kg, and 144.5 +/- 30.2 kg, respectively (T1 < DJ; p < 0.05). These data suggest that DJ performed before 1RM testing may enhance squat performance in trained male athletes.     

Effects of age on testosterone responses to resistance exercise and musculoskeletal variables in men

This study compared serum total testosterone (TT) and free testosterone (FT) responses of young (20-26 years, n = 8), middle-aged (38-53 years, n = 7), and older (59-72 years, n = 9) men to resistance exercise. We also examined the relationships between testosterone (T) levels and strength, bone mineral density (BMD), and body composition variables for each age group. Subjects were tested for isotonic muscular strength (1 repetition maximum [1RM]), BMD (dual-energy x-ray absorptiometry [DXA]) and body composition (DXA). Each group performed an acute exercise protocol (3 sets, 10 repetitions, 80% of 1RM, 6 exercises). Blood samples were obtained at baseline, immediately postexercise, and 15 minutes postexercise for the TT and FT assays. The older age group had significantly (p < 0.05) lower T levels than the young group, but each group exhibited an increase (p < 0.05) in TT and FT immediately postexercise. Total T and FT were significantly correlated (p < 0.05) with strength in middle-aged and older men and with bone-free lean tissue mass in older men. In conclusion, middle-aged and older men showed similar relative T responses to those of younger men to a single bout of high-intensity resistance exercise. However, T levels were related to strength and muscle mass only in middle-aged or older men. On a practical application level, older men can complete a high-intensity resistance exercise program resulting in spikes in T that may attenuate age-related muscle and BMD loss.     

Effects of three-day bed rest on metabolic, hormonal and circulatory responses to an oral glucose load in endurance or strength trained athletes and untrained subjects.

The study was designed to find out (1) whether the effect of 3-day bed rest on blood glucose (BG) and plasma insulin (IRI) responses to glucose ingestion depends on preceding physical activity and (2) whether plasma adrenaline (A), noradrenaline (NA) and cardiovascular changes following a glucose load are modified by bed rest. Eleven sedentary students (22.5+/-0.3 yrs), 8 long distance runners (18.6+/-0.3 yrs) and 10 strength trained athletes (21.2+/-2.1 yrs) were examined before and after bed rest. Plasma IRI, BG, NA, A, heart rate (HR), and blood pressure (BP) were measured during 2 hrs following glucose (75 g) ingestion. The responses of BG and IRI to glucose load were calculated as incremental areas under the curves (auc). Both in athletes and untrained subjects bed rest markedly increased IRIauc, while BGauc was elevated only in sedentary subjects (p<0.05). The greatest increases in IRIauc and IRI/BG ratios were found in the endurance athletes. The data from all subjects (n = 29) revealed that the initial plasma NA and glucose-induced increases in NA and A were lowered after bed rest (p < 0.01). These effects were most pronounced in the endurance athletes. Bed rest did not influence HR or BP in any group. It is concluded that (1) the athletes have more adequate compensation for the bed-rest-induced decrement in insulin sensitivity than sedentary men; (2) three-day bed rest diminishes basal sympathetic activity and attenuates sympathoadrenal response to oral glucose; (3) endurance athletes have greater sympathetic inhibition than strength athletes or sedentary men.     

Effect of a proprietary protein supplement on recovery indices following resistance exercise in strength/power athletes

The effect of 42 g of protein ingested pre- and post-exercise on recovery from an acute resistance exercise session was examined in 15 male strength/power athletes who were randomly divided into a supplement (SUP) or placebo (PL) group. Subjects reported to the Human Performance Laboratory (HPL) on four separate occasions (T1–T4). Maximal strength [one repetition-maximum (1-RM)] testing was performed during T1. During T2 subjects performed four sets of ten repetitions at 80% of their 1-RM in the squat, dead lift and barbell lunge exercises with 90 s of rest between each set. Blood draws occurred at baseline (BL), immediate and 15 min post-exercise to determine testosterone, cortisol and creatine kinase (CK) concentrations. Subjects reported back to the HPL 24 (T3) and 48 h (T4) post-exercise for a BL blood draw and to perform four sets of ten repetitions with 80% of 1-RM for the squat exercise only. No differences in the number of repetitions performed in the squat exercise were seen between the groups at T2. Relative to T2, PL performed significantly (P < 0.05) fewer repetitions than SUP at T3 and T4 (−9.5 ± 5.5 repetitions vs. −3.3 ± 3.6 during T3, respectively, and −10.5 ± 8.2 repetitions vs. −2.3 ± 2.9 repetitions during T4, respectively). No differences in hormonal measures were seen between the groups. CK concentrations were significantly (P < 0.05) elevated at T3 for both groups, but continued to elevate (P < 0.05) at T4 for PL only. No significant group differences were noted for CK at any time point. Results indicate that a proprietary protein SUP consumed before and after a resistance training session significantly contributes to improvements in exercise recovery 24 and 48 h post-exercise.