Kay, Tony; Blazevich, Tony; Giakas, Giannis; Hooton, Andy; Akehurst, Sally; Mina, Minas A. (University of DerbyCollege of Science and Engineering, 2020-09-08)
      Warm-up routines are typically designed to precondition the neuromuscular system for enhanced performance and reduced injury risk during subsequent high-intensity physical activities, including during strength training. As such, identifying an effective warm-up routine to augment muscular performance is of clear importance to strength (and other) coaches and athletes. Incorporating variable resistance (VR) via the use of chains or elastic bands during strength training alters the loading characteristics during exercises to impose a greater mechanical stimulus, however the impact of VR on subsequent free-weight exercise performance is unknown. Therefore, the aims of this thesis were to examine the acute effects of conditioning VR exercise compared to free-weight resistance (FWR) exercise on subsequent one-repetition maximum (1-RM) back squat and countermovement vertical jump (CMJ) height performance after the performance of a comprehensive, test-specific warm-up, and to examine possible alterations to mechanics and neuromuscular activity underpinning any changes. Techniques including 3D motion analysis, electromyography (EMG) and ground reaction force measurement were used in three studies on recreationally active volunteers experienced in squatting and jumping. In Study 1, significantly greater 1-RM squat-lift load (6.2 ± 5.0%; p < 0.01) and mean eccentric-phase knee extensor EMG amplitude (32.2 ± 6.7%; p < 0.01) were found after the chain-loaded resistance (CLR) warm-up, where an increasing load is applied as the subject raises their body with the load, compared to the FWR condition. However, no statistical differences (p > 0.05) were detected in concentric phase EMG, knee angular velocity or peak knee flexion angle. Thus, performing a CLR warm-up enhanced subsequent free-weight 1-RM performance without kinematic changes; these data were considered to indicate a real 1-RM increase as the mechanics of the lift were not influenced. Study 2 followed an identical methodological design, however elastic bands were used to provide an inexpensive, portable, easily-implemented, and therefore more practical method of altering the load-time characteristics of the squat lift through VR. Significantly greater 1-RM squat load (7.7 ± 6.2%; p < 0.01) with lower peak and mean eccentric (16–19%; p < 0.05) and concentric (12–21%; p < 0.05) knee angular velocities were found after the elastic band (EB) warm-up compared to the FWR condition. As EB resistance evoked greater mean improvements in squat performance than the CLR used in Study 1, the influence of FWR and EB squat exercises following a comprehensive warm-up were compared using a more functional, CMJ, task at different post-exercise time points (i.e. 30 s, 4 min, 8 min, and 12 min) (Study 3). No changes in any variable were found after the FWR warm-up (p > 0.05). However, statistical (p < 0.05) and practically-meaningful increases were detected in CMJ height (5.3-6.5%), net impulse (2.7-3.3%), take-off velocity (2.7-3.8%), peak power (4.4-5.9%), kinetic (7.1-7.2%) and potential (5.4-6.7%) energy, peak normalised rate of force development (12.9-19.1%), peak concentric knee angular velocities (3.1-4.1%) and mean concentric vastus lateralis (VL) EMG activity (27.5-33.4%) at all time points after the EB warm-up condition. Thus, when a complete CMJ-specific warm-up was provided, FWR squat had no additional effect on CMJ performance however the alteration of the squat lift force-time characteristics using EB led to a substantial CMJ enhancement. The findings from the present series of studies have important implications for research study design as the warm-up imposed and the resistive modality selected appear to influence subsequent movement performances, i.e. 1-RM back squat or CMJ performances. In previous studies, standardised (or no) warm-up protocols imposed before the baseline testing have been associated with subsequent enhancements in squat lift and CMJ performances following conditioning contractions, although it is unclear whether this is a consequence of acute neuromuscular alteration relating to the conditioning contractions or to the warm-up itself. Collectively, the present findings, show that physical performance can be enhanced in at least some conditions by application of conditioning contractions even after completion of a comprehensive, test-specific warm-up, which have important practical implications in the formulation of pre-performance warm-up routines where maximal force production is an important goal.
    • The influence of caffeine expectancies on simulated soccer performance and perceptual states

      Hooton, Andy; Sheffield, David; Higgins, Matthew; Shabir, Akbar (University of DerbyThe University of Derby, School of Human Sciences, 2020-10)
      Caffeine (CAF) is the most widely consumed ergogenic substance in sport and has been reported to improve various attributes associated with successful soccer performance including, endurance capacity, gross motor skill performance and cognitions. These benefits are typically ascribed to pharmacological mechanisms (i.e. central nervous and peripheral tissue stimulation). However, the psychological and perceptual permutations that are associated with CAF expectancies are largely unaddressed in most experimental designs but could be as important as CAF pharmacology in understanding if/how CAF elicits an ergogenic response on sport performance. As the consumption of pharmacologically active CAF may not be necessary in observing a CAF associated ergogenic response, this body of work may prove beneficial to individuals suffering from pre-existing health concerns (e.g. hypertension, genetic polymorphisms, depression, insomnia etc.), CAF habituation, and those participating in late evening sports competitions whereby CAF consumption may impair sleep quality/duration. The main aim of this thesis is to evaluate and explore the psychobiological effects of expectancies associated with oral CAF consumption on various facets of simulated soccer performance and perceptual states. This was achieved via completion of the following objectives: (1) conducting a systematic review and meta-analyses pertaining to literature exploring the potential psychobiological effects of CAF on sport and exercise (A) and cognitive performance (B) (2) exploration of the potential psychobiological effects of CAF on high-intensity intermittent endurance capacity, reaction time and soccer skill proficiency (3) exploration of the potential psychobiological effects of CAF on perceptual fatigue and mood states (4) exploration of the potential psychobiological effects of CAF on subjective perceptions using the double-dissociation design but in particular the mixed methods approach (Brooks et al., 2015). There remains a severe under representation of the mixed methods design in the literature pertaining to the phenomenon of CAF expectancies on sport, exercise, and cognitive performance. The mixed methods design and associated triangulation of quantitative and qualitative data is fundamental to validly compare CAF’s psychological versus pharmacological impetus. Prior to this thesis, only two other studies (Beedie et al., 2006; Duncan et al., 2009) implemented the mixed methods design, with neither providing a rigorous account of methodological decisions, researcher reflexivity, and/or evidence of applying an epistemological framework. These factors were incorporated within the current thesis and improved the quality of data collection, analysis, and reflection. The results of our, novel, meta-analyses demonstrated that all studies exploring the psychobiological effects of CAF on sport and exercise performance displayed a beneficial effect (p=0.01) with an overall moderate effect size (Cohen’s d (ES): 0.40) observed. In contrast, no significant effect was observed for studies exploring the psychobiological effects of CAF on cognitive performance (p=0.142) with a small effect size (ES=0.1) observed. Though, due to significant methodological heterogeneity associated with studies exploring the psychobiological effects of CAF on cognitive performance, any associated implications here should be taken with caution. Experimental study 1 explored the influence of CAF expectancies on facets of simulated soccer performance (e.g. exercise capacity, reaction time and passing ability (LSPT)) and perceptual states via utilisation of a mixed-methods approach and double-dissociation design. Exercise capacity was greater (p<0.05) for CAF psychology (given placebo (PLA)/told CAF) (623 ± 117 s) versus pharmacology (given CAF/told PLA) (578 ± 99 s) with all participants running longer during psychology. This benefit appeared to be driven by CAF expectancies and reductions in perceptual effort. Interestingly, positive perceptions for told CAF conditions appeared to impair BATAK performance via potential CAF over reliance. In contrast, negative perceptions possibly facilitated BATAK performance via augmented conscious effort. A similar trend to BATAK was observed for LSPT performance. Following the completion of experimental study 1 it became apparent that the techniques used to modulate expectancies across experimental conditions (i.e. told PLA/CAF groups) here or any other study with a primary aim of exploring the influence of CAF expectancies on sport, exercise and/or cognitive performance, require validation. This was the premise of experimental study 2. No meaningful findings were observed from baseline to post-intervention across any outcome measure during experimental study 2. This lack of effect may be related to environmental factors, whereby individuals completed trials in classrooms and/or a home cinema, prior to lectures/seminars and/or social interactions, respectively. In contrast, participants in experimental study 1 were administered the appropriate expectancy modulating techniques after they had perceived to consume PLA or CAF within an environment that necessitated an immediate importance for CAF (e.g. prior to exercise performance). In summary, the novelty and original contribution of the current body of research entails: completion of a systematic review and meta-analyses pertaining to the influence of CAF expectancies on sport, exercise and cognitive performance; assessment of the influence CAF expectancies may have on simulated soccer performance; the implementation of a mixed methods approach and double dissociation design; an in depth rationale, description and set of instructions for the utilisation of the mixed methods approach in any future research, including the use of an epistemological framework; a summary of ecological factors that are fundamental in understanding the phenomenon of CAF expectancies across sport and exercise performance. With respect of the main findings from the experimental data contained in this thesis: the benefits associated with CAF expectancies may better suit tasks that entail lesser cognitive/skill specific attributes but greater gross motor function (e.g. cycling, weightlifting, running etc.) and this is likely due to reduced perceptual effort. Moreover, future studies aiming to validate expectancy modulating techniques or generally assessing expectancies should provide a greater immediate importance for CAF and this may be achieved by replicating environmental and/or psychosocial conditions associated with sport performance (e.g. the utilisation of a performance measure) and the perception for CAF consumption.