Changes in muscle CSA and force production of leg extensors during combined strength and endurance training in young men and women : is there any order effect?

Abstract

In many sports strength training improves performance significantly more than bare sport specific training. Combined strength and endurance (SE) training can lead to similar cardiorespiratory and musculoskeletal adaptations compared to strength (S) or endurance (E) training alone. When both training types are performed in the same training session, strength training performed immediately after endurance training (E+S) may hinder strength development and improve endurance performance more than the opposite order (S+E). The purpose of this study was to investigate differences between S+E and E+S training during a 24-week combined training period in muscle CSA and force production. A total of 32 men and 26 women participated to this study. Subjects were randomly assigned to four groups: men S+E, men E+S, women S+E, women E+S (mS+E, mE+S, wS+E, wE+S) and they performed two 12 weeks training periods with measurements at weeks 0(pre), 12(mid) and 24(post). Measurements included neuromuscular (1RM, isometric strength, MVC500, power), cardiorespiratory (VO2max, time to exhaustion) and muscle size (ultrasound, DXA) measurements. Subjects trained twice a week during weeks 0–12 and five times in two weeks during weeks 13–24. In the first training period the strength training included loads of 40–60% (weeks 0–2) 60–80% (weeks 3–7) and 80–95% (weeks 8–12) of 1RM. The endurance training included two different training sessions. The first training session included continuous cycling around the aerobic threshold for 30–45min, whereas the second training session was interval training. The training program both for strength and endurance was similar during training period 2, but the loads were increased based on the development. All training groups improved significantly 1RM (all groups p<0.001), isometric strength (mS+E and wS+E p<0.01, mE+S and wE+S p<0.001), MVC500 (mS+E, mE+S and wS+E p<0.01, wE+S p<0.001), power (mS+E p<0.001, mE+S, wS+E and wE+S p<0.01), time to exhaustion (all groups p<0.001), CSA (VL50% (mS+E p<0.001, mE+S, wS+E and wE+S p<0.01), and lean mass of legs (all groups p<0.001) during the 24-week training period. In VO2max all except mE+S improved significantly (mS+E and wS+E p<0.01, wE+S p<0.05). In the ultrasound measurement wE+S increased CSA in VL50% significantly more than wS+E (18.7±11.2% vs. 8.8±8.7%, p<0.05) and mE+S (18.7±11.2% vs. 10.4±8.4%, p<0.05). In time to exhaustion, wE+S improved significantly more than mE+S (21.7±10.9% vs. 13.1±8.6%, p<0.05). According to this study, muscle CSA, muscle strength and endurance performance improved with combined single session strength and endurance training independently of the training order. In addition, wE+S showed larger muscle hypertrophy (CSA) than that of observed when training by the opposite order and larger than in men using the same E+S order.