Similar hormonal responses to concentric and eccentric muscle actions using relative loading.

Conventional resistance exercise is performed using sequential concentric (CON) and eccentric (ECC) contractions, utilizing the same muscle load. Thus, relative to maximal CON and ECC resistance, the ECC contraction is loaded to a lesser degree. We have recently shown that at the same absolute load, CON contractions are associated with greater growth hormone (GH) but similar total testosterone (TT) and free testosterone (FT) responses compared with ECC contractions and attributed the larger GH response to greater relative CON loading. In the present study, we have examined the same endocrine parameters to six different upper and lower body exercises using relative loading rather than absolute loading, hypothesizing that GH responses would be similar for CON and ECC actions, but TT and FT responses would be greater after ECC contractions. Seven young men with recreational weight training experience completed an ECC and CON muscle contraction trial on two different occasions in a counterbalanced fashion. The exercises consisted of four sets of 10 repetitions of lat pull-down, leg press, bench press, leg extension, military press, and leg curl exercises at 65% of an ECC or CON 1-RM with 90 s between sets and exercises. CON and ECC actions were performed at the same speed. ECC 1-RMs were considered to be 120% of the CON 1-RM for the same exercise. Blood samples were collected before, immediately after, and 15 min after the exercise. GH significantly increased across both trials but was not different between the two trials. Total testosterone was not significantly altered in response to either trial; however, free testosterone concentrations increased in response to both ECC and CON trials. Data suggest that CON and ECC muscle contractions produce similar GH, T, and free testosterone responses with the same relative loading.

Ghrelin and other glucoregulatory hormone responses to eccentric and concentric muscle contractions.

OBJECTIVE: Heavy resistance exercise increases growth hormone (GH) and blood glucose levels. Ghrelin is an endogenous ligand for the GH secretagory receptor that stimulates growth hormone release. Circulating ghrelin levels are suppressed by insulin and glucose. The study was conducted to determine effects of concentric (CON) and eccentric (ECC) muscle actions at the same absolute workload on circulating ghrelin and glucose as well as related glucoregulatory peptides. METHODS: Ten-RM loads for bench press, leg extension, military press, and leg curl were obtained from nine males, mean age 25. +/- 1.2 yr and body fat 17.2 +/- 1.6%. Subjects then completed two experimental trials of either CON or ECC contractions at the same absolute workload. Subjects performed four sets of 12 repetitions for each exercise at 80% of a 10-RM with 90 s rest periods. A pulley system or steel levers were positioned on each machine to raise or lower the weight so only CON or ECC contractions were performed. Pre-, post-, and 15-min post-exercise blood samples were collected. RESULTS: Ghrelin did not increase in response to either muscle action and actually declined during the CON trial. Glucose and insulin increased regardless of the form of muscle action, but amylin and C-peptide did not change. CONCLUSIONS: Data indicate that ghrelin does not contribute to moderate resistance exercise-induced increases in growth hormone, whether from CON or ECC muscle actions. Results suggest that with a moderate loading protocol both CON and ECC muscle actions performed at the same absolute workload elevate glucose and insulin concentrations, but are not related to post-CON exercise ghrelin suppression.

Rigorous running increases growth hormone and insulin-like growth factor-I without altering ghrelin.

It has been suggested that ghrelin may play a role in growth hormone (GH) responses to exercise. The present study was designed to determine whether ghrelin, GH, insulin-like growth factor-I (IGF-I), and IGF-binding protein-3 (IGFBP-3) were altered by a progressively intense running protocol. Six well-trained male volunteers completed a progressively intense intermittent exercise trial on a treadmill that included four exercise intensities: 60%, 75%, 90%, and 100% of Vo2max. Blood samples were collected before exercise, after each exercise intensity, and at 15 and 30 mins following the exercise protocol. Subjects also completed a separate control trial at the same time of day that excluded exercise. GH changed significantly over time, and GH area under the curve (AUC) was significantly higher in the exercise trial than the control trial. Area under the curve IGF-I levels for the exercise trial were significantly higher than the control trial. There was no difference in the ghrelin and IGFBP-3 responses to the exercise and control trials. Pearson correlation coefficients revealed significant relationships between ghrelin and both IGF-I and IGFBP-3; however, no relationship between ghrelin and GH was found. In conclusion, intense running produces increases in total IGF-I concentrations, which differs from findings in previous studies using less rigorous running protocols and less frequent blood sampling regimens. Moreover, running exercise that produces substantial increases in GH does not affect peripheral ghrelin levels; however, significant relationships between ghrelin and both IGF-I and IGFBP-3 exist during intense intermittent running and recovery, which warrants further investigation.

Leptin and steroid hormone responses to exercise in adolescent female runners over a 7-week season.

The purpose of the study was to investigate the responses of leptin and steroid hormones to maximal exercise in adolescent female runners over a competitive season. Seven adolescent female distance runners completed three testing trials during weeks 1.4 and 7 of their high-school track season. Blood samples were collected before and after a discontinuous graded exercise test to exhaustion (GXT) for each trial. Tests were administered during the subjects' normal training time (3:30 p.m.-5:00 p.m.). Compared to week 1, peak O2 uptake rose significantly during the season and was 10% and 7% higher at weeks 4 and 7, respectively. Levels of dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), cortisol, testosterone, and leptin increased significantly in response to the graded exercise tests. Testosterone levels were also changed over the course of the study. Resting testosterone levels and testosterone responses to exercise in weeks 4 and 7 were both higher than in week 1. Resting concentrations and acute increases of the other hormones were not changed over the season. It appears, therefore, that DHEA, DHEAS, cortisol, testosterone and leptin concentrations increase in response to running in adolescent female runners. Data also suggest that training and/or maturation increases resting testosterone concentrations and testosterone responses to running in adolescent female runners during a training season.

Circuit weight training and its effects on excess postexercise oxygen consumption.

OBJECTIVE: There is a paucity of research concerning energy expenditure during and after circuit weight training (CWT). There is evidence that duration of rest between sets affects metabolic responses to resistive exercise. The purpose of the study was to determine the effect of rest-interval duration upon the magnitude of 1 h of excess postexercise oxygen consumption (EPOC). METHODS: Seven healthy men completed two randomized circuit weight training sessions using 20-s and 60-s rest intervals (20 RI, 60 RI). Sessions included two circuits of eight upper and lower body resistive exercises in which 20 repetitions were performed at 75% of a previously determined 20 repetition maximum. RESULTS: The 1 h EPOC of 10.3 +/- 0.57 L for the 20 RI session was significantly higher than 7.40 +/- 0.39 L for the 60 RI session. The net caloric expenditure during 1 h of recovery from the 20 RI session was significantly higher than that of the 60 RI session (51.51 +/- 2.84 vs 37.00 +/- 1.97 kcal); however, total gross energy expenditure (exercise + 1 h recovery) was significantly greater for the 60 RI protocol (277.23 kcal) than the 20 RI protocol (242.21 kcal). CONCLUSION: Data demonstrate that shortening the rest interval duration will increase the magnitude of 1 h EPOC from CWT; however, the exercise + recovery caloric costs from CWT are slightly greater for a longer rest interval duration protocol. These data suggest that total caloric cost be taken into account for CWT.

Effects of aerobic exercise on serum leptin levels in obese women.

It has been demonstrated that leptin concentrations in obese patients may be altered by weight loss. We examined the effects of a 9-week aerobic exercise program on serum leptin concentrations in overweight women (20-50% above ideal body mass) under conditions of weight stability. Sixteen overweight women, mean (SE) age 42.75 (1.64) years, comprised the exercise group which adhered to a supervised aerobic exercise program. A graded exercise treadmill test was conducted before and after the exercise program to determine maximal oxygen uptake (VO2max) using open-circuit spirometry. The women demonstrated improved aerobic fitness (VO2max increased 12.29%), however, body fat and the body mass index did not change significantly [42.27 (1.35)-41.87 (1.33)%]. Fourteen women, age 40.57 (2.80) years, did not exercise over the same time period and served as a control group. Serum leptin levels were not significantly altered for either the exercise [28.00 (2.13)-31.04 (2.71) ng x ml(-1)] or the control group [33.24 (3.78)-34.69 (3.14) ng x mg(-1)]. The data indicate that 9 weeks of aerobic exercise improves aerobic fitness, but does not affect leptin concentrations in overweight women.

Serum leptin concentrations in response to acute exercise in postmenopausal women with and without hormone replacement therapy.

The purpose of the study was to examine the effects of acute exercise and hormone replacement therapy on serum leptin concentrations in postmenopausal women. Subjects were 15 healthy, postmenopausal women, 8 on hormone replacement therapy (HRT) and 7 not on hormone replacement therapy (NHRT). Group comparisons indicated no significant differences between HRT and NHRT groups with respect to age, height, weight, BMI, sum of skinfolds, or VO2max, and verified significant differences in estradiol and FSH concentrations. After an overnight fast, each subject completed 30 min of treadmill exercise at approximately 80% VO2max. Over 2 hr and 10 min, baseline, exercise, and recovery blood samples were collected from an intravenous catheter. A control session conducted a month later consisted of the same blood sampling protocol without exercise. Leptin concentrations declined significantly over the course of both the exercise and control sessions, gradually decreasing from baseline levels to -1.54 +/- 0.49 ng. ml-1 postexercise, and continuing to decline to a low of -2.89 +/- 0.59 ng. ml-1 at the end of the session. There was no significant difference between groups with respect to this decline. This is the first study to document that diurnal changes in leptin concentrations in postmenopausal women are not altered by acute treadmill exercise or HRT status. The study underscores the need to account for a diurnal reduction in leptin over the course of an exercise trial.

Practice schedule effects on the performance and learning of low- and high-skilled students: an applied study.

This study examined the effects of practice schedule manipulations implemented in an instructional setting on the performance and learning of low- and high-skilled students. College undergraduates (N = 83) enrolled in 5 tennis classes completed a pretest on the forehand and backhand ground strokes, practiced these skills under a blocked or alternating schedule, and then completed a posttest. Results indicated that practice schedule effects on learning were influenced by student ability. Low-skilled students assigned to the blocked schedule had higher posttest scores than those assigned to the alternating schedule, whereas no significant differences were found for high-skilled students. These findings are discussed in relation to previous applied and laboratory-based findings and as a means for manipulating practice difficulty in teaching physical education.

Effects of a learning model and augmented feedback on tennis skill acquisition.

This experiment investigated the effects of observing a learning model and receiving augmented verbal feedback on the acquisition and retention of the tennis volley. Female undergraduate students were randomly assigned to four groups: (a) AFB--received augmented verbal feedback from an instructor, (b) LMFB--monitored a learning model's trials and feedback, (c) LMFB+AFB--monitored a learning model's trials and feedback and received verbal feedback from an instructor, and (d) Control--received neither treatment. Subjects were pretested, given 50 acquisition trials, and then a retention test. Outcome and movement pattern dependent variables were employed. Repeated measures analyses indicated that all three experimental groups were significantly better than the Control group on movement pattern and outcome, with the greatest success experienced by the LMFB+AFB group. Findings are discussed relative to previous research findings and implications for practitioners.