Neuromuscular adaptations to single-session combined strength and endurance training in untrained men : an examination of the order effect

Abstract

Understanding the adaptations to single-session combined strength (S) and endurance (E) training has received increased attention in scientific literature through the expand-ing use of combined training programs for practical purposes. However, the intra-session exercise order when performing both E and S in the same training session may limit potential strength development, as the neuromuscular adaptations to either training mode alone are very different. Research on the effect of the intra-session exercise order of combined training on various training-induced adaptations, i.e. the order effect, is currently limited, especially with regard to the neuromuscular adaptations. Therefore, the purpose of this study was to investigate the order effect to single-session combined strength and endurance training on the long-term neuromuscular adaptations.

Thirty-two young adult male subjects (29 ± 4 years) completed a 24-week progressive single-session combined strength and endurance-training program. The subjects were split into two groups performing opposite intra-session exercise orders, endurance be-fore strength (E+S; n = 14) or strength before endurance (S+E; n= 18) by pairwise matching of basal maximum strength results. All subjects were tested on three separate occasions (0, 12 and 24 weeks). A group of subjects (n = 8) participated in a two-week control period performed before week 0 (-2 to 0 weeks) to ensure reproducibility and stability of important dependent variables. Maximal voluntary activation (VA), surface electromyography (sEMG), one-repetition maximum concentric strength (1-RM), maximal voluntary isometric force (MVC) and rapid force production (AV500) of the leg extensors and flexors were evaluated.

No changes occurred in strength during the two-week control period, while after the 24-week training period significant increases in 1-RM load of 13% (p<0.001) and 17% (p<0.001), knee extension MVC of 7% (p<0.05) and 14% (p<0.01) and leg press MVC of 15% (p<0.01) and 13% (p<0.01) were observed for E+S and S+E, respectively. There were no significant between group differences in strength gains. After 24 weeks a significant increase took place in VA of quadriceps femoris of 4% (p<0.01) in S+E only whereas no significant changes occurred in E+S. There were differences between groups in changes in maximum sEMG activity of the vastus lateralis after 24 weeks as large increases took place in S+E whereas non-significant changes occurred in E+S.

The present data provide some evidence of an order effect on training induced adapta-tions to combined strength and endurance training. Maximum voluntary activation of trained leg muscles appeared to be interfered after training E+S when compared to S+E. Additionally, strength development appeared to be affected by training order as larger strength gains were continually observed for S+E when compared to E+S, however, strength gains were not statistically significant. These findings highlight the importance of combined training order as the level or neural activation governs muscular strength.