Increased rate of force development during periodized maximum strength and power training is highly individual

Maximum strength training induces various improvements in the rate of force development (RFD) on a group level, but no study has investigated inter-individual adaptations in RFD. Fourteen men (28 ± 6 years old) performed the same 10-week maximum strength and then a 10-week power training program. Maximal force and RFD were recorded during maximal isometric leg extension voluntary contractions repeatedly before every 7th training session (2 sessions/week). After the intervention, subjects were retrospectively divided into three groups based on their RFD improvements: (1) improved only during the maximum strength period (MS-responders, + 100 ± 35%), (2) improved only during the power period (P-responders, + 53 ± 27%) or (3) no improvement at all (non-responders, + 3 ± 9%). All groups increased dynamic 1RM equally, but baseline 1RM was greater (p < 0.05) in responder vs non-responder groups. MS-responders had higher electrical stimulation-induced torque at baseline and they improved (+ 35 ± 28%) power production at 50% 1RM load more than P- (- 7 ± 20%, p = 0.052) and non-responders (+ 3 ± 6%, p = 0.066) during the maximum strength training period. MS-responders increased vastus lateralis cross-sectional area (+ 12 ± 9%, p < 0.01) as did P-responders (+ 10 ± 7%, p = 0.07), whereas non-responders were unchanged. Free androgen index (FAI) in responders was higher (+ 34%, p < 0.05) compared to non-responders at baseline. The maximum strength period decreased testosterone (- 17 ± 12; 17 ± 22%), FAI ratio (- 12 ± 14; - 21 ± 23%) and testosterone/cortisol ratio (- 17 ± 25; - 31 ± 20%) in MS and P-responders, respectively. During the P-period hormonal levels plateaued. To conclude, periodized strength training induced different inter-individual physiological responses, and thus RFD development may vary between individuals. Therefore, RFD seems to be a useful tool for planning and monitoring strength training programs for individual neuromuscular performance needs.