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Resistance Training/Periodization

(11) Muscular Fatigue Following Resistance Exercise to Failure at High Loads in Oral Contraceptive Pill Users

Friday, July 12, 2024
12:30 PM – 2:00 PM East Coast USA Time
Location: Exhibit Hall
Abstract Details: Neuromuscular fatigue is characterized by diminished force production, increased perceived effort, and increases in muscle excitation during fatiguing exercise. Much of the existing knowledge contributing to our understanding of fatigue is derived primarily from male participants, limiting the generalizability of findings to females.  In addition, 70% of NCAA female athletes use some form of hormonal contraceptive. However, little is known about the influence of hormonal contraceptives on fatiguing exercise performance.

Purpose: This study examined performance fatigability and neuromuscular responses across three weeks of a 28-day oral contraceptive pill (OCP) cycle (W1: placebo pill week; W2: week 1 or 2 of active pills; W3: week 3 of active pills) during fatiguing, higher intensity resistance exercise.

Methods: Eight college-aged females (age=23±5 yrs, body mass=68.0±17.2 kg, hheight=163.7±8.4 cm) using monophasic OCPs participated in this study. The participants performed a one-repetition maximum (1RM) for the deadlift, followed by repetitions to failure at 70% 1RM throughout 3 weeks of the OCP cycle. The participants completed pre- and post-exercise maximal voluntary contractions (MVC) to determine absolute strength (pre-MVC) and performance fatigability (%∆ pre- to post-exercise MVC). The electromyography (EMG) of the bicep femoris muscle was recorded from the right limb during all visits to examine amplitude (AMP) and mean power frequency (MPF) responses during the repetitions to failure and were normalized to the 1RM as a percent for data analysis. Separate, one-way repeated measures ANOVAs were run to examine changes in absolute strength, repetitions completed, and performance fatigability across the OCP cycle. Separate, 3 (week: W1, W2, W3) x 2 (time: first 10% repetitions completed, last 10% repetitions) repeated measures ANOVAs were run to examine changes in EMG AMP and MPF during repetitions completed to failure. Significance was set at p< 0.05 for all analyses.

Results: There was no significant one-way ANOVA for absolute strength (W1: 125±32 kg, W2: 126±25 kg, W3: 119±34 kg, p=0.196), repetitions completed (W1: 15±4 reps, W2: 15±5 reps, W3: 15±3 reps, p=0.845), or performance fatigability (W1: 30±17%, W2: 34±15%, W3: 31±23%, p=0.708). For EMG AMP, there was no significant interaction (F(2,14)=1.640, p=0.229, pη2=0.190) or main effect of week (p=0.587). There was a main effect of time (F(1,7)=81.260, p< 0.001, pη2=0.921) that indicated EMG AMP during the first 10% of repetitions completed (90±33%) was less than the final 10% (117±40%). For EMG MPF, there was no interaction (F(2,14)=0.156, p=0.857, pη2=0.022) or main effect of week (p=0.859) or time (p=0.224).

Conclusion: Absolute strength, repetitions completed to failure, and performance fatigability are unaffected by OCP cycle week. While EMG AMP increased over time, indicating increases in muscle excitation, EMG AMP and MPF were not impacted by OCP cycle week during the deadlift exercise performed to failure at 70% 1RM. These findings indicate that an exogenous form of estrogen/progesterone does not impact muscular performance or neuromuscular responses. PRACTICAL APPLICATION: Coaches and practitioners should continue to program resistance exercise based on the goals and needs of their athletes and clients. The week an OCP user is at in their pill cycle does not appear to influence performance during higher intensity resistance exercise. 

Acknowledgements: None