Isometric Mid-thigh Pull Variables That Are Responsive To Performance Decrements Following High Volume Resistance Exercise

High volume resistance exercise acutely reduces muscular performance, commonly identified through reductions in maximal force production. The Isometric Mid-Thigh Pull (IMTP) has been used to assess these changes after resistance exercise, though to date, 33 different variables have been identified during an IMTP. It is unclear which of these variables should be used to assess acute performance loss following resistance exercise. PURPOSE: Identify which IMTP variables are responsive to performance decrements induced through high volume exercise. METHODS: 10 recreationally trained women (21 ± 2 yrs; 62.3 ± 5.1 kg; 1.62 ± 0.07 m; 1.23 ± 0.17 kg·kg body mass-1) completed eight sets of 10 repetitions at 70% of their one-repetition maximum (1RM) in the back squat. On visit one, women provided informed written consent and completed a back squat 1RM. Qualifying women (1RM ≥ 1.0x body mass) returned to the lab ≥72 hours later to complete the 8x10 squat protocol. IMTP was assessed prior to (PRE), as well as immediately (IP), one- (1H), 24- (24H) and 48- (48H) hours after exercise. The average of three IMTP pulls was used for analysis. Previously used IMTP measurements, including rate of force development (RFD), peak force (PF), time specific force and impulse were assessed over a range of time bands (e.g. 0-30 ms, 0-50 ms, 0-100 ms). Data were analyzed via Mixed Model Regression with time as a fixed factor. RESULTS: A time effect was noted for PF over five seconds (F = 3.72; p = 0.020) with reductions in PF from PRE (756 ± 187 N) at IP (679 ± 155 N; p = 0.003) and 1H (676 ± 183 N; p = 0.039). A time effect was observed for force at 150 ms (F = 3.45; p = 0.032) with reductions from PRE (446 ± 199 N) at 1H (318 ± 130 N; p = 0.029) and 24H (293 ± 157 N; p = 0.009). A time effect was also noted for force at 200 ms (F = 3.87; p = 0.024) with reductions from PRE (520 ± 189 N) at 1H (384 ± 129 N; p = 0.010) and 24H (354 ± 158 N; p = 0.004). A time effect was observed for force at 250 ms (F = 3.91; p = 0.022) with reductions in force from PRE (565 ± 188 N) at 1H (426 ± 121 N; p = 0.008) and 24H (407 ± 149 N; p = 0.005). No time effects were noted for any other IMTP variables. CONCLUSION: Data indicate PF over five seconds as well as time specific forces at 150, 200 and 250 ms are responsive to acute performance changes after high volume exercise and should be the variables used to quantify performance decrements.