James L. Tryniecki

Hormonal responses from concentric and eccentric muscle contractions

UNLABELLED Intense resistance exercise can acutely increase testosterone (T), free testosterone (FT), and growth hormone (GH) concentrations, but there are few investigations concerning acute endocrine responses to concentric (CON) and eccentric (ECC) contractile actions. PURPOSE The purpose of the study was to compare acute anabolic hormonal responses to bouts of dynamic CON and ECC contractions from multiple exercises at the same absolute load. METHODS Ten young men (age: 24.7 +/- 1.2 yr, weight: 85.45 +/- 24.2 kg, and height: 178 +/- 0.2 cm) completed two trials in counterbalanced fashion consisting of only CON or ECC contractions at the same absolute workload. Subjects performed four sets of 12 repetitions of bench press, leg extension, military press, and leg curl at 80% of a 10-repetition maximum with 90-s rest periods. Blood samples were collected pre-, post-, and 15-min postexercise. RESULTS There were significant increases in GH, T, and FT and lactate for both trials, but only GH and lactate were greater for the CON trial. CONCLUSION CON exercise increases GH concentrations to a much greater extent than ECC exercise at the same absolute load, and it is likely that greater GH responses were related to intensity rather than mode of contraction. Also, CON and ECC dynamic contraction trials at the same absolute workload elicited similar small but significant increases in T and FT, indicating that the greater metabolic stress produced by during the CON trial did not affect these hormone responses.

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.

Maximal eccentric and concentric strength discrepancies between young men and women for dynamic resistance exercise.

Although research has demonstrated that isokinetic eccentric (ECC) strength is 20–60% greater than isokinetic concentric (CON) strength, few data exist comparing these strength differences in standard dynamic resistance exercises. The purpose of the study was to determine the difference in maximal dynamic ECC and CON strength for 6 different resistance exercises in young men and women. Ten healthy young men (mean ± SE, 25.30 ± 1.34 years), and 10 healthy young women (mean ± SE, 23.40 ± 1.37 years) who were regular exercisers with resistance training experience participated in the study. Two sessions were performed to determine CON and ECC 1 repetitions maximum for latissimus pull-down (LTP), leg press (LP), bench press (BP), leg extension (LE), seated military press (MP), and leg curl (LC) exercises. Maximal ECC and maximal CON strength were determined on weight stack machines modified to isolate ECC and CON contractions using steel bars and pulleys such that only 1 type of contraction was performed. Within 2 weeks, participants returned and completed a retest trial in a counterbalanced fashioned. Test-retest reliability was excellent (r = 0.99) for all resistance exercise trials. Men demonstrated 20–60% greater ECC than CON strength (LTP = 32%, LP = 44%, BP = 40%, LE = 35%, MP = 49%, LC = 27%). Womens strength exceeded the proposed parameters for greater ECC strength in 4 exercises, p < 0.05 (LP = 66%, BP = 146%, MP = 161%, LC = 82%). The ECC/CON assessment could help coaches capitalize on muscle strength differences in young men and women during training to aid in program design and injury prevention and to enhance strength development.

Follicular and luteal phase hormonal responses to low-volume resistive exercise.

The purpose of the study was to 1) determine the effects of a low-volume resistive exercise protocol on serum concentrations of estradiol (E2), progesterone (P4), growth hormone (GH), testosterone (T), and androstenedione (AN) and 2) ascertain whether the endocrine responses are affected by the phase of the menstrual cycle. Eleven untrained, healthy women were assigned to either an early follicular or luteal testing group. The subjects completed three sets of bench press, lat-pull, leg extension, and leg curl exercises at a 10 repetition maximum load on fixed machines with 2-min of rest between sets. Blood samples were collected through an indwelling cannula before, during, and after the exercise. Area-under-the-response-curve (AUC) data demonstrated that E2 concentrations were significantly elevated in both follicular and luteal phases with a greater response in the luteal phase. Moreover, data suggest there is a luteal phase-induced increase in GH and AN in response to the low-volume resistive exercise; however, P4 and T concentrations in untrained women are not increased by low-volume resistive exercise with 2-min rest periods, nor does the altered hormonal milieu produced by the phase of the menstrual cycle affect these hormonal responses.