The Performance and Physiological Responses of Soccer Substitutes on Match-day

This thesis aimed to elucidate current practices and practitioner perceptions regarding the match-day activities of soccer substitutes, assess physiological and performance responses to current practices, and implement a substitute-specific match-day intervention in an applied scenario. Survey findings (chapter three) and empirical observations indicated that substitutions are typically made at half-time or later, often to increase the pace of play and/or change team tactics. Practitioners highlighted the importance of pre-pitch-entry preparations for allowing substitutes to positively influence matches, noting preparatory strategies as a crucial research area (chapter three). Perhaps due to regulatory and practical constraints, and despite delays of ~75-120 min following cessation of the pre-match warm-up before pitch-entry, chapter four showed that professional substitutes typically perform minimal activity (~3 rewarm-up bouts·player-1·match-1) prior to match-introduction. When replicated in controlled conditions (chapter five), such practices failed to maintain body temperature (~1.6% decrease) and physical performance capacity (~3.9-9.4% decrease) from an initial warm-up until simulated second-half pitch-entry. Transient changes in physical outputs were recorded after actual match-introduction, but evidence of performance limiting fatigue was absent during ~30 min of simulated match-play. Although substitutes often perform post-match ‘top-up’ conditioning sessions to help maintain favourable physical loads, contextual factors influenced session demands (chapter six). Crucially, chapter seven showed that modified practices that included substitutes 1) performing a new pre-match warm-up alongside members of the starting team, 2) participating in a staff-led half-time rewarm-up, and 3) receiving education emphasising the value of substitutes and the efficacy of (re)warm-up activities, increased the activity completed pre-pitch-entry whilst appearing to benefit post-pitch-entry physical performance responses and potentially match scoreline differentials. Practitioners and policy-makers should therefore consider assessing current preparatory strategies for substitutes and, where necessary, modifying existing practice. Given the barriers existing on match-day, ensuring appropriate exposure to additional high-speed activities throughout a training week may also be important.