Differential neuromuscular adaptations following multi-joint vs single-joint resistance exercise training

We combined ultrasound, EMG and dynamometry measurements to establish differences in neuromechanical adaptations following two resistance training programs of equal training volume, one involving a multi-joint exercise and the second a single-joint exercise. Twenty-four participants were divided into a squat group (SQG) and a leg extension group (LEG). Both groups performed ten weeks of training. Before and after the training protocol, muscle architecture of the knee extensors was quantified in vivo using an ultrasound apparatus. The vastus lateralis (VL) torque-fascicle length relationship was also obtained. The maximum isometric torque (Tmax), the maximum EMG activity and the optimal VL fascicle length (L₀) were determined. A significant increase in 1RM (P < 0.001) was observed in both groups post-training. Muscle thickness increased in both groups (P = 0.008 and P < 0.001 LEG and SQG, respectively), but the increase was greater in SQG than LEG (P = 0.031). Both groups showed significant changes in Tmax (P = 0.0084 and P = 0.0044 for LEG and SQG, respectively) and the improvement in T_max was larger (P = 0.041) for SQG (+ 14%) than LEG (+ 10%). Pennation angle, fascicle length and VL L₀ increased post-training in SQG only. A transfer effect of 1RM was observed in both groups: SQG improved the leg extension 1RM by about 16%, whereas LEG increased the squat 1RM by about 9%; SQG showed a larger strength improvement transfer than LEG (P = 0.037). Due to the high knee torque required to maintain a given external load, squat exercise training may be more effective than the leg-extension setup used in the present study in eliciting neuromuscular adaptations.