| Abstract | Introduction: Athletic populations are underrepresented in literature, with a majority of studies examining the effect of acute and chronic training in untrained individuals. The training adaptations gained following resistance or endurance training may alter performance, specifically, the inherent fatigue resistance observed in females. However, limited data exists examining sex differences in fatigue during dynamic muscle actions commonly performed during resistance training. Therefore, this dissertation examines neuromuscular responses between sexes during acute resistance exercise in resistance- and endurance-trained athletic populations. Additionally, this work identifies the musculoskeletal adaptations that occur across a year of training in Collegiate Division 1 football players.
Methods: Three studies were completed in highly trained, athletic populations, examining neuromuscular differences in males and females during acute training in the upper body and lower body, and musculoskeletal adaptations to chronic training in Collegiate Division I football players. The first study utilizes electromyography (EMG) to examine neuromuscular responses during acute resistance exercise and subsequent isometric force production of the elbow flexors in a resistance-trained population. The second study uses EMG and ultrasonography of the knee extensors and examines neuromuscular responses during acute resistance exercise and subsequent isometric force production in an endurance-trained population. The third study identifies musculoskeletal adaptations in Collegiate Division 1 football players across the 2023 year.
Results: At the same relative intensity (50% 1RM), resistance-trained females demonstrate statistically significant greater fatigue resistance in the elbow flexors, quantified by a greater number of repetitions performed (M: 48.3 ± 6.1; F: 64.9 ± 12.3), greater subsequent isometric strength maintenance (M: 69.8%; F: 76.1%), and greater relative biceps brachii EMG amplitude (M: 98.6 ± 31.1%; F: 125.8 ± 36.9%) compared to males. However, endurance-trained males and females demonstrate no difference in the number of repetitions performed (M: 69.3 ± 17.1; F: 72.6 ± 26.5) or subsequent isometric force produced (M: 86.6%; F: 88.1%) during knee extension. Despite the lack of performance differences, females demonstrate greater maintenance of relative rectus femoris EMG amplitude (M: 73.38 ± 6.39%; F: 93.23 ± 5.61%) compared to males during the knee extension task. Lastly, Division 1 Collegiate football players demonstrate significant changes in lean mass and fat-free mass index (FFMI), observing increases (177.0 ± 24.5 lbs; 24.1±2.1 kg/m2) and decreases (172.6 ± 25.3 lbs; 23.5 ± 2.3 kg/m2) that corresponds with increased or decreased training volume, respectively. This occurred without a significant change in body fat percentage (16.5 ± 7.4% to 17.2 ± 7.6%) or body weight (226.5 ± 48.5 lbs to 223.2 ± 49.3 lbs). However, bone mineral composition significantly increased (9.2 ± 1.2 lbs to 9.4 ± 1.3 lbs) and Achilles tendon echo intensity decreased (123.8 ± 15.7 a.u. to 99.64 ± 17.3 a.u.), while Achilles tendon thickness generally maintained size (0.47 ± 0.08 cm to 0.50 ± 0.06 cm) regardless of changes in training volume.
Conclusions: Sex differences in acute resistance training fatigue are more pronounced for the upper limbs compared to the lower limbs. Additionally, similar neuromuscular responses are observed between males and females for the knee extensors, unlike that shown for the elbow flexors. Collegiate Division 1 football players present significant lean mass changes due to alterations in training, demonstrating modifications in lean mass despite chronic training experience. This dissertation presents novel information regarding prior training experience on acute resistance training fatigue between males and females. Additionally, novel insights are shown for the effect of training over a year of collegiate football on musculoskeletal variables and emphasize the use of FFMI and Achilles tendon ultrasonography in collegiate football players. This data shows the neuromuscular and musculoskeletal responses to acute and chronic exercise training in athletic populations. |
