The mechanical, hormonal and metabolic responses to two resistance loading schemes

Crewther, Blair Tehira
Keogh, Justin
Cronin, John
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Master of Health Science
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Auckland University of Technology

The effective prescription of resistance exercise for strength and power development has been a source of debate amongst practitioners and sport scientist alike. One of the key issues in this area relates to the training load that would best facilitate strength and power adaptation. Heavy loads (>60-70% 1RM) have been traditionally used for maximal strength development by facilitating changes in neural function (strength) and muscle size (hypertrophy). However, many studies have now found lighter load (>45%1RM) training equally effective in improving both strength and hypertrophy. Similarly, many studies have found heavy load training effective in enhancing various measures of power though lighter loads (e.g. 45% 1RM) are thought to maximise the mechanical power output of muscle. Realising that adaptation depends upon some interaction between the mechanical, hormonal and metabolic stimuli, examining these responses would enhance our understanding of the underlying determinants of strength and power, and thereby improve strength and conditioning practice. Therefore, the purpose of this study was to examine the mechanical, hormonal and metabolic responses to equal volume light and heavy loading schemes. Eleven males (mean 26.6 ± 6.7 years; mean 79.0 ± 8.1 kg) with a minimum of 12 months weight training experience each performed two exercises (Smith squat and supine squat) at a light (45% 1RM) and heavy (88% 1RM) intensity. The light scheme consisted of eight sets of six repetitions, with six sets of four repetitions performed in the heavy scheme. Rest periods of three and four minutes respectively were used. Saliva sampling was used to determine the hormonal (cortisol and testosterone) and metabolic (lactate) responses. Samples were collected at rest (pre-), immediately after the first exercise (mid-), at the conclusion of the second exercise (P0) and every 15 minutes thereafter for one hour (P15, P30, P45, P60). Mean values for all variables were analysed with a paired sample T-test. Chances that the true effects were substantial (% and qualitative) were also calculated. No significant (P>0.05) difference in total forces was found between schemes; however, the light scheme produced significantly greater total time under tension (36%), total work (37%) and total power output (115%). Total impulse (38%) was the only variable found to be greater in the heavy scheme. A decrease in testosterone (TST) was observed in the heavy scheme (-4 to -29%) with no significant changes found across the light scheme (1 to 12%). Cortisol decreased in the light (-6 to -30%) and heavy (-14 to -44%) schemes until P45. An increase in the TST/cortisol ratio was observed in both the light (17 to 49%) and heavy (2 to 44%) schemes. Both loading schemes resulted in similar increases in lactate (0.3 to 1.0nmol/l). Equating two schemes by volume resulted in differential responses, many of which favoured the lighter scheme in terms of mechanical, hormonal and metabolic outputs. These findings suggest that load or intensity employed may be not as important as initially proposed and that other factors (e.g. volume, technique) may explain the similar strength and hypertrophy adaptation reported in studies comparing light and heavy schemes.

Isometric exercise , Kinematics , Exercise Science
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