| Summary: | Previous research has documented positive effects of periodised muscular endurance resistance training in untrained men and women. Therefore, the overarching objective of this thesis was to compare the efficacy of two resistance training progression models [linear periodisation (LP) vs. undulating periodisation (UP)], and to elucidate the best method to vary the exercise stimulus to develop muscular endurance in trained youth athletes. With respect to the overarching objective of this thesis, a series of studies were conducted. The first aim was to identify the reliability and sensitivity of neuromuscular function variables in trained youth athletes. Second, to investigate acute neuromuscular function, endocrine and perceptual wellbeing responses following two different muscular endurance resistance training sessions [3 sets of 25 repetition maximum (RM) and 3 sets of 15RM]. Lastly, to investigate the effects of two distinct resistance training models (LP vs. UP) on selected performance, physiological and psychological variables in trained youth team sports athletes. Also, the different physiological, neuromuscular, perceptual wellbeing responses within this process were described and implications for athlete monitoring discussed. It was found that the reliability and sensitivity of neuromuscular function variables was unique to the population in question. Specifically, only countermovement jump mean force [CMJMF; smallest worthwhile change (SWC) = 2.7%, coefficient of variation (CV) = 1.0%)], countermovement jump mean power (CMJMP; SWC = 3.2%, CV = 2.7%), countermovement jump peak power (CMJPP; SWC = 3.4%, CV = 3.0%) and plyometric push up mean force (PPMF; SWC = 2.9%, CV = 2.2%) displayed acceptable reliability (CV < 5%) and sensitivity in field hockey youth athletes. Next, neuromuscular function, endocrine and perceptual wellbeing measures, obtained from trained youth participants, maintained similar acute biological responses irrespective of muscular endurance resistance training protocols. Force and power measures (CMJMF, CMJMP, CMJPP and PPMF) improved (p ≤ 0.05) 48 hours following both muscular endurance resistance training programmes. At 72 hours, testosterone: cortisol ratio (T:C ratio) showed a moderate increase [effect size (ES) = 0.72] following the 15RM protocol whereas a small decrease (ES = 0.41) was observed after the 25RM session. Overall perceptual wellbeing, fatigue and soreness scores reflected changes in neuromuscular function, while stress, sleep and mood did not show any differences. Finally, muscular endurance tests demonstrated that UP (back squat ES = 1.62; bench press ES = 1.77) was more efficacious than LP (back squat ES = 0.69; bench press ES = 1.72). Resting salivary testosterone concentration increased in the UP (31.47%) compared to LP (- 8.73%) group, whereas salivary cortisol concentration and T:C ratio remained unchanged. Session rating of perceived exertion (session RPE), mood and stress scores were frequently higher during training phase II and III compared to phase I. No changes were detected in neuromuscular function. Overall, this thesis offered several practical applications from the findings. First, the reliability and sensitivity of neuromuscular function variables were population specific. As such, practitioners are encouraged to establish the reliability and determine the neuromuscular function variable/s within the group to be trained. Second, as fatigue is multifaceted, practitioners should not rely on a single monitoring approach and incorporate both physiological and psychological aspects to monitor resistance training. Lastly, practitioners working with team sports athletes and intending to develop muscular endurance, can employ UP, performed in conjunction with sport specific training. Most importantly, it is highly advantageous to integrate a suitable monitoring measure, to direct appropriate sequencing of training loads, to result in optimal athletic performance.
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