Resistance Training Proximity To Failure And Responses Of Neuroprotective Biomarkers

PURPOSE: This study compared the acute and chronic responses of brain-derived neurotrophic factor (BDNF), cathepsin B (CatB), insulin-like growth factor-1 (IGF-1), and interleukin-6 (IL-6) to three resistance training programs terminating sets at different proximities to failure. METHODS: Twenty eight resistance-trained men (age: 22.38 ± 2.96 yrs, body mass: 80.43 ± 10.97 kg, height: 174.60 ± 6.23 cm, training age: 4.45 ± 2.67 yrs) trained the back squat and bench press 3 days/wk, on non-consecutive days, for 6 weeks. The only difference between groups was the proximity to failure of each set (4-6 repetitions in reserve-RIR, n = 9; 1-3 RIR, n = 10; and 1-3+ RIR, n = 9). In the 1-3+ group the final set of the bench press during each session was trained to failure; however, the final set of the squat was performed to a non-standardized submaximal RIR in an effort to prevent injury. Serum was collected immediately before and after training on day 1 of weeks 1 and 6. Linear mixed effects models were fit with fixed effects and interactions thereof, for group, time, and exercise separately for all biomarkers. RESULTS: For all biomarkers, the three-way interaction (exercise × time × group) was not statistically significant (p = 0.20 to 0.62). Additionally, there were no significant main effects or two-way interactions for IGF-1 (p > 0.05). However, there were significant time effects for BDNF (p = 0.005) and IL-6 (p < 0.001), indicating that both biomarkers increased acutely from pre- to post-exercise in week 1 (BDNF: +4.2%; IL-6: +54.8%) and week 6 (BDNF: +10.9%; IL-6: +63.2%) collapsed across groups. For CatB, a significant exercise × time (p = 0.002) interaction was observed, indicating differences in the acute change of CatB in week 6 (+11.7%) vs. week 1 (-5.6%). CONCLUSIONS: In summary, acute multi-joint RE far from or close to failure can confer a BDNF response. This investigation is the first to demonstrate the potential for acute RE to transiently increase CatB after 6 weeks of training.