Time kinetics of acute changes in muscle architecture in response to resistance exercise

Objectives: The study aimed to assess acute changes in muscle architecture and its recovery after exhaustive exercise. We hypothesised that repetitive leg press exercise would decrease vastus lateralis fascicle length, while increasing both muscle thickness and pennation angles. By investigating the time kinetics of recovery of these parameters, we wished to gain insight into the mechanisms responsible for muscle architectural changes during exercise. Design: Muscle architecture was assessed in 41 male volunteers (25.2 ± 3.7 yrs; 1.78 ± 0.06 m; 76.4 ± 11.7 kg) before and directly after, as well as 5, 10, 15, and 30 min after induction of fatigue by leg press exercise. Method: Vastus lateralis muscle thickness, pennation angles and fascicle lengths were measured at rest by ultrasonography. Muscular fatigue was induced by an exhaustive series of maximum power, single leg press repetitions. Results: Following leg press exercise vastus lateralis muscle thickness and pennation angles were increased by approximately 7 and 10%, whereas fascicle lengths decreased by 2%. Different recovery times (muscle thickness: 30 min; pennation angles: 15 min; fascicle lengths: 5 min) were observed. Conclusions: The differential time courses of recovery suggest that changes in muscle thickness, pennation angles, and fascicle lengths are driven by different exercise-related stimuli. Increased muscle perfusion and tendon creep are likely candidates accounting for short-term changes in muscle architecture.