Factors affecting paced exercise: how is pacing strategy influenced?

In recent years exercise pacing research has identified numerous factors that can influence exercise intensity and improve overall performance. However, the list of factors that can influence pacing is far from comprehensive or extensively researched. Subsequently, this thesis aimed to investigate pacing factors which have not yet been empirically or functionally tested. Specifically, the following aspects were identified for investigation; the role of exercise experience, exercise-induced pain, and athlete motivation during competition. These factors were chosen for both the crucial role they play within theoretical pacing models and for the way they influence different aspects of exercise pacing (i.e. variables that are internal and external to the athlete during exercise, as well as prior to exercise). By selecting different factors, this ensured a holistic approach was taken to investigating the theoretical pacing literature. The first factor investigated was an athlete's prior experience of the exercise, which is vital to anticipatory regulation of the task at hand and consequently, the development of a pacing strategy. Secondly, exercise-induced pain was chosen, as this a factor that is internal to the athlete during exercise. This sensation is key to the models of pacing and plays a significant role in exercise regulation. However, transcutaneous electrical nerve stimulation has not yet been fully tested as a method to reduce exercise-induced pain and how this can impact performance. Lastly, competition is an external factor during exercise, which has been known to influence pacing and performance for many years. However, the physical presence of competitors in ecologically valid circumstances, as well as interplay of social and physiological factors have not been rigorously investigated. Study one. Exercise performance is reproducible in experienced athletes; however, less trained participants exhibit greater variability in performance and pacing. To reduce variability, it is common practice to complete a familiarization prior to experimental testing. However, there are no clear guidelines for familiarizing novice participants to a cycling time-trial (TT), and research findings from novice populations may still be influenced by learning effects. Accordingly, the aims of this study were to establish the variability between TTs after administering differing familiarization protocols (duration or type) and to establish the number of familiarization trials required to limit variability over multiple trials. Thirty recreationally active participants, with no prior experience of a TT, performed a 20-km cycling TT on five separate occasions, after completing either a full (FF, 20-km TT, n=10), a half (HF, 10-km TT, n=10) or an equipment familiarization (EF, 5-min cycling, n=10). Variability of TT duration across five TTs was the lowest after completing FF (P = 0.69, ηp2 = 0.05) compared to HF (P = 0.08, ηp2 = 0.26) and EF (P = 0.07, ηp2 = 0.21). In the FF group after TT2, the effect size for changes in TT duration was small (d < 0.49). There were large differences between later TTs in HF (d = 1.02, TT3-TT4) and EF (d = 1.12, TT4-TT5). The variability in mean power output profiles between trials was lowest within FF, with a similar pacing profile reproduced between TT3-TT5. Familiarization of the exercise protocol influenced the reproducibility of pacing and performance over multiple, maximal TTs, with best results obtained after a full experience of the exercise compared to HF and EF. The difference of TT1 to later TTs indicates that one familiarization is not adequate in reducing the variability of performance for novice participants. After the FF and an additional TT, performance changes between TTs were small. However, a reproducible pacing profile was not developed until after the FF and two additional TTs. These findings indicate that a minimum of three full familiarizations are necessary for novice participants to limit systematic error before experimental testing. Study two. Afferent information from exercising muscle contributes to the sensation of exercise-induced muscle pain. Transcutaneous electrical nerve stimulation (TENS) delivers low–voltage electrical currents to the skin, inhibiting nociceptive afferent information. The use of TENS in reducing perceptions of exercise-induced pain has not yet been fully explored. This study aimed to investigate the effect of TENS on exercise-induced muscle pain, pacing strategy and performance during a 5-km cycling time trial (TT). On three separate occasions, in a single-blind, randomized and crossover design, 13 recreationally active participants underwent a 30-min TENS protocol, before performing a 5-km cycling TT. TENS was applied to the quadriceps prior to exercise under the following conditions; control (CONT), placebo with sham TENS application (PLAC), and an experimental condition with TENS application (TENS). Quadriceps fatigue was assessed with magnetic femoral nerve stimulation assessing changes in potentiated quadriceps twitch force at baseline, pre and post exercise. Subjective scores of exertion, affect, and pain were taken every 1-km. During TTs, application of TENS did not influence pain perceptions (P = 0.68, ηp2 = 0.03). There was no significant change in mean power (P = 0.16, ηp2 = 0.16) or TT duration (P = 0.17, ηp2 = 0.14), although effect sizes were large for these two variables. Changes in power output were not significant but showed moderate effect sizes at 500-m (ηp2 = 0.10) and 750-m (ηp2 = 0.10). Muscle recruitment as inferred by electromyography data was not significant but showed large effect sizes at 250-m (ηp2 = 0.16), 500-m (ηp2 = 0.15) and 750-m (ηp2 = 0.14). This indicates a possible effect for TENS influencing performance up to 1-km. Yet, overall, these findings do not support the use of TENS to improve 5-km TT performance. Study three. The aim of this study was to investigate time-trial (TT) performance in the presence of one competitor and in a group with competitors of various abilities. In a randomized order, 24 participants performed a 5-km cycling TT individually (IND), with one similarly matched participant (1v1), and in a group of four participants (GRP). For the GRP session, two pairs of matched participants from the 1v1 session were used. Pairs were selected so that TT duration was considered either inferior (INF) or superior (SUP) compared to the other pair of participants. Overall, TT duration (P = 0.86, ηp2 < 0.01) was not different between conditions, whilst heart rate (HR) was significantly greater in GRP compared to IND (P < 0.01, ηp2 = 0.16). For INF, a large effect size for both mean power (P = 0.07, ηp2 = 0.15) and HR (P = 0.05, ηp2 = 0.16), indicates greatest effort in GRP. Pacing behaviour was affected by competition but similar in 1v1 and GRP for SUP, whilst large effect sizes indicate an increased power output in the initial 750-m for INF in GRP. Additionally, for INF, there was a significant correlation with ego orientation for an increase in TT duration between the GRP session and both the IND (r = 0.43, P = 0.04) and 1v1 (r = 0.54, P = 0.01) sessions. For INF participants, the intensity was increased when competing in GRP. Yet, the presence of the SUP competitors resulted in lesser performance improvements for ego oriented INF participants. These findings demonstrate that consideration should be given to the ability of competitors in a group setting to provide adequate motivation. Overall this thesis provides novel insight into pacing factors that have previously not been fully understood. This research is of importance as a greater understanding of how exercise is self-regulated is crucial to unlocking the potential for increased exercise performance. The main results and conclusions of this thesis shed light on the highlighted pacing factors of experience, exercise-induced pain and competition, and how these can impact on performance during self-paced cycling time-trials. Accordingly, these findings provide information to benefit the development of sound experimental protocols as well as providing a mechanistic understanding of the development of exercise scenarios and interventions that can be beneficial to performance outcomes.