The effect of different accentuated eccentric load levels in eccentric-concentric loading contractions on acute neuromuscular, growth hormone and blood lactate responses during a hypertrophic protocol

Abstract

When accentuated load is applied during the eccentric (ECC) phase of eccentric-concentric (ECC-CON) contractions, it is defined as dynamic accentuated external resistance (DAER) exercise. This study monitored acute neuromuscular responses, growth hormone (GH) and blood lactate (La) concentrations to find out the most efficient ECC-CON loading strategy for muscle hypertrophy by employing various DAER resistances in the bench-press. Male subjects (age=32.4±4.3years, n=11) were assigned as subjects. The measurements consisted of 4 “hypertrophic” sessions separated by 5-6 days recovery. The subjects performed 4 sets of 10 repetitions with 2 min recovery between the sets. The resistances were 70%, 80%, 90% and 100% of 1 RM for the ECC phase and 70% RM was constantly used for the CON phase. Muscle EMG, growth hormone (GH) and blood lactate (La) were measured at pre and post conditions in ISOM bench press and EMG was measured also in the 2nd (pre) and last (post) repetitions in dynamic measurements. ECC force was systematically smaller in the 70% condition than in the other conditions (P<0.001). Significant reductions in ISOM pre to post peak force occurred in all conditions (P<0.01-0.001). CON force reduced from pre to post loading in all conditions (P<0.001). Pre to post change in La in the 90% condition (9.5±2.3mmol/l) was greater (P<0.05) than in the 70% condition (7.7±1.1mmol/l). The highest individual pre to post change in La was larger after the 90% (p<0.001) condition compared to La after the control condition. No significant differences were observed in absolute mean post GH and in GH/repetition concentrations between the conditions. ECC EMG of the agonists increased with the increase in load but was significant only in deltoid anterior (P<0.01). A significant relationship (P<0.05) was observed between optimal ECC load and 1RM/bodymass-ratio (R=0.85). The major findings in the present study were the higher change of La in the 90% condition compared to the 70% condition (P< 0.05) and the high correlation between the optimal ECC load and 1RM/BM-ratio. The findings can be applied into practice in designing optimal exercise protocols in training for muscle hypertrophy and suggest the importance of individualised load selection for DAER exercises.