Abstract:

Decreased rate of force development (RFD) post-exercise is an important indicator for performance reduction in sports and daily life, and it has been previously shown in both the exercised and non-exercised limbs. Explanations for reduced RFD in the non-exercised limb (i.e., crossover) are plausibly due to centrally-mediated factors. While many studies have focused on the crossover effect of fatigue with a wide variety of muscle action types (e.g., isotonic, isometric, isokinetic), few focused on the changes in RFD in the contralateral (unexercised) limb. PURPOSE: The purpose of this study was to examine how concentric and eccentric muscle actions to failure in the dominant arm elbow flexor (EF) would affect RFD in the contralateral EF. METHODS: Fifteen subjects consented to participate in the randomized crossover within-subjects design. Participants reported to the lab for 10 visits (i.e., familiarization, concentric, eccentric, and control) followed by 24hr and 48hr follow-up visits. Participants performed concentric and eccentric dominant arm dumbbell exercise for 6 sets to task failure with loads corresponding to 25% and 30% of maximal voluntary isometric contraction (MVIC) strength, respectively. Exercise was set at a cadence of 1-second up/down for each repetition and the investigator manually removed and replaced the dumbbell accordingly. The control visit included no exercise. Dominant (exercised) and non-dominant (contralateral) RFD at the time interval of 0-50 (RFD₅₀) ms from onset was measured at pre-, immediate-post, 24hr- and 48hr-post for all visits. Two-way ANOVAs for the dominant (exercised) and non-dominant (non-exercised) arm (condition [eccentric, concentric, control] ´ time [RFD₅₀] were performed with an a set at 0.05. RESULTS: Significant main effects for time at RFD₅₀ were revealed for the non-dominant arm. Follow-up tests revealed significantly lower RFD for immediate-post compared to 48hr-post (mean + standard error (SE): 443.16 + 138.76 vs. 556.14 vs. 144.53 Nm×s^-1). Significant main effects for condition and time were revealed for dominant arm RFD₅₀. Follow-up tests showed significant lower RFD (collapsed across condition) for immediate-post compared to pre (mean + SE; immediate-post vs. pre: 297.65 + 82.51 vs. 570.69 + 153.18 Nm×s^-1) and to 24hr-post (mean + SE; immediate-post vs. 24hr-post: 297.65 + 82.51 vs. 474.29 vs. 117.61 Nm×s^-1). CONCLUSIONS: For early onset RFD the non dominant arm was unaffected by dominant arm exercise, and regardless of condition, early onset RFD was decreased immediate-post and remained decreased for up to 24hr-post in the dominant arm. PRACTICAL APPLICATIONS: Gaining a greater understanding of how differing exercise modes affect RFD has implications for several populations (e.g., young, old, athlete, non-athlete). This study provides specific evidence that concentric and eccentric exercise cause similar decreases in early onset RFD directly after exercise and up to 24hrs after in the young non-athletic population. Thus, when designing a resistance training program for this population trainers and practitioners can incorporate specific eccentric exercise for enhancing strength with the understanding that it will affect rapid force production ability similar to concentric exercise.