Recovery response comparisons between variable resistance and long and short muscle length isometric exercise

Isometric exercises at long muscle length (LML) and short muscle length (SML), and variable resistance (VAR) exercises, are effective to achieve neuromuscular and morphological adaptation. To date, no studies have compared pectoralis major muscle recovery after these modalities. Therefore, this study aimed to compare the muscle damage and recovery after LML, SML, and VAR in trained men. Twelve participants (age: 25 ± 4 y, height: 178 ± 7 cm, body weight: 82 ± 10 kg, training experience: 7 ± 4 y) completed the protocols in a random order with a 10-day washout period. Assessments occurred pre-exercise (BL) and at 15 min (P-15 min), 24 h (P-24 h), and 48 h (P-48 h) post-exercise, evaluating muscle thickness (MT), echo intensity (EI), isometric peak force, average power at bench press throw power test (BPT), and muscle soreness. Blood samples were also collected at BL and at P-24 h, and creatine phosphokinase (CPK) was measured. Changes in MT at P-15 min and P-24 h were more elevated following VAR compared to SML and LML (p = 0.003; η²_p = 0.271). No condition × time interactions were found for EI (p = 0.233), peak force (p > 0.319), BPT (p = 0.614), and muscle soreness (p = 0.115). The EI, peak force, and BPT parameters returned to baseline at P-24 h, while muscle soreness persisted for 48 h without any significant differences between protocols. All exercise protocols resulted in similar elevations of CPK (p = 0.727; 387 ± 159, 396 ± 199 and 362 ± 170 U/L for LML, SML and VAR, respectively). In conclusion, all exercise protocols cause muscle damage. However, the mechanical and metabolic stress of VAR may prolong the recovery of initial muscle architecture compared to LML and SML.