The effect of concurrent resistance and repeated-sprint exercise on performance and the cytokine response in female team-sport athletes
Repeated-sprint ability (RSA), power and strength are regarded as fundamental physical attributes for team-sport athletes. Investigations of concurrently training these fitness qualities, particularly in well-trained female team-sport athletes are scarce. The primary purpose of this thesis was the improvement of team-sport performance in female athletes through concurrent resistance (RT) and RSA training, concentrating on acute and chronic training structure. With recent interest in inflammatory cytokines in sports science, the cytokine response to concurrent exercise was also investigated with the aim of effectively measuring internal training load. The mechanism of action of interleukin (IL)-6, the most commonly researched cytokine in sports science, was also investigated.
Chapters 4 and 5 measured performance and magnitude of change in inflammatory cytokines and endocrine hormones to single mode or concurrent RT (6 × 6 sets of back squat exercise at 80 % 1-repetition maximum, sets separated by 3 min rest 2) and RSA (4 × 6 sets of 20 m maximal shuttle sprints, sets separated by 3 min rest) exercise of different intra-session exercise order (exercise modes separated by 15 min rest). It was found that exercise intensity and duration were important factors in the exercise induced cytokine and endocrine hormone response to exercise as significant alterations in these bio-markers were only seen following concurrent exercise (Chapter 5) and not during single-mode RT and RSA exercise (Chapter 4). There did not appear to be evidence of acute interference or residual fatigue present during the concurrent exercise protocol as intra-session exercise order did not affect maximal squat or sprint performance, or rating of perceived exertion in response to either mode of exercise. Exercise order showed minor differences in a small number of bio-markers.
Chapters 6 and 7 investigated the effects of 4 weeks of concurrent RT and RSA training, performed either on the same day (SDT: in a single session, 3 sessions per week) or alternating days (ADT: 6 sessions per week, each separated by 24h) on performance and systemic and skeletal muscle physiological responses to an acute concurrent RT/RSA protocol (protocol identical to RT:RSA exercise performed in Chapter 5). Both training structures were found to significantly increase RSA total time, sprinting, jumping and maximal strength performance. Interestingly, training structure (SDT or ADT) had no significant effect on the magnitude of these increases despite large differences in rest periods (15 minutes vs. 24 hours) between the exercise modes perhaps suggesting that the volume of the acute stimulus is less important than the total volume of training. The acute concurrent RT and RSA protocol (both pre- and post-training) significantly altered systemic and local cytokines, hormones and signalling proteins within 180 minutes of the recovery period. However, training appeared to have no effect on the majority of these responses with only serum cortisol and plasma glucose concentrations significantly lowered by training. The failure of the inflammatory response to attenuate with training suggests that current understanding of cytokines and their role in the immediate post-exercise period is unclear and thereby reduces their effectiveness to provide information about training load.
IL-6 is the dominant cytokine responding prior to other anti-inflammatory cytokines in response to exercise and is also thought to play a role in exercise metabolism via the regulation of glucose output from the liver. In Chapter 8 a new method for measuring the role of IL-6 on hepatic glucose output (HGO) was tested using exercised human plasma and an isolated rat liver model. Results from Chapter 8 provide information suggesting that IL-6 may not increase HGO at rest or during exercise and may even negatively regulate HGO, in contrast to current theory.
The concurrent RT and RSA protocol employed throughout this thesis was shown to be an effective training stimulus to produce large increases in performance variables in female team-sport athletes in a short training period irrespective of exercise order or training structure. Based on the results of these studies and until the physiological role of the inflammatory cytokines elevated by acute exercise but unaltered by training are more clearly understood, it is not yet worthwhile for sport science practitioners to invest in cytokine monitoring in team-sport athletes for the measurement of training load.