The effect of exercise-induced pain on endurance performance, and strategies to mitigate its impact

Exercise-induced pain (EIP) is a natural consequence of exercising intensely, and results due to an accumulation of endogenous algesic substances, an increase in muscular pressure and muscular distortion or tissue damage. However, the presence of EIP may have negative consequences for exercise and endurance performance, brought about by the physiological and/or psychological effect of pain. EIP has not been widely addressed in sport and exercise science research, and much of the contemporary literature has ignored its potential role in endurance exercise performance, despite the wide acknowledgement it gains in interviews with athletes, coaches, exercise scientists and health and fitness practitioners. Therefore, more empirical research needs to be completed that explores the role of EIP in endurance performance, and the physiological and/or psychological contribution it may make to fatigue and work rate regulation. Therefore, the main purpose of this thesis was to examine the effect of EIP on endurance exercise performance, and identify strategies to mitigate its impact in various endurance exercise tasks. Consequently, this thesis consists of 5 experimental studies, as outlined below. The 1st experimental study (Chapter 3) assessed the relationship between traditional experimental measures of pain (the cold pressor test (CPT) and algometry), EIP tolerance and participants' performance of a 10 mile (16.1 km) cycling time trial. The primary finding was that no correlation was found between experimental pain measures and TT performance (mean pain in CPT; R = 0.222; time lasted in the CPT; R = -0.292; PPT; R = -0.016). However, there was a significant correlation between EIP tolerance and TT performance (R = -0.83, P 0.05). The ANOVA also revealed a significant main effect of condition for exercise-induced pain during the TTE test (P = 0.035). No significant changes in rating of perceived exertion (RPE) were found between the three conditions (P > 0.05). A 3 x 8 (condition x iso-time) ANOVA revealed a significant interaction effect for exercise-induced pain over time between conditions during the TTE test with lower pain intensity in the TENS and IFC conditions (F (3.4, 58.4) = 3.671, P = 0.013). No interaction and main effects for RPE were found between the three conditions (P > 0.05). For the MVC, paired-sample t-tests demonstrated that MVC was significantly reduced following the TTE in the Sham (t (17) = 9.069, P 0.05). No significant differences in mean RPE were found between conditions during the TT (P > 0.05). Interestingly, this study also showed that TENS elicits an analgesic effect on EIP and improves the TT performance, whereas IFC technique does not elicit any reduction of EIP and consequently has no effect on whole-body endurance performance. This experiment demonstrated the first time that TENS intervention significantly improved completion time of the cycling TT, and that this was attained by the cyclists sustaining a greater power output (PO), heart rate (HR) and blood lactate (B[La]). Regardless of the increased physiological stress and metabolic rate induced by the higher PO, participants perceived EIP in the TENS strategy alongside in the absence of a difference in RPE between conditions. The improvement in dynamic endurance was probably the result of reduction in EIP for a given load. This is the first experiment showing that a TENS intervention can be used to elicit this analgesia to EIP, and suggests that there may be scope for TENS to be used during exercise in those where EIP negatively effects their engagement in physical activity. The final experiment in this thesis (Chapter 7) examined the effect of mood and emotional state on EIP and endurance performance. The use of painful images prior to endurance cycling performance was used to negatively affect mood, which was hypothesised to increase EIP. The primary finding was that the ANOVA revealed a significant difference in completion time between conditions (F (2, 40) = 8.480, P = 0.001). Pairwise comparisons revealed that participants performed a significantly faster TT (P = 0.003) in the pleasant condition (29 min 38 s ± 4 min 35 s) and the neutral condition (29 min 39 s ± 3 min 34 s) compared to the painful condition (30 min 19 s ± 5 min 7 s). There were no significant differences between the neutral condition and the pleasant (P = 1.000). The ANOVA also revealed a significant difference in PO (F (2, 40) = 6.318, P = 0.004), mean HR ((F (2, 40) = 4.502, P = 0.017) and mean B[La] (F (2, 40) = 5.724, P = 0.007) between conditions during ?the TT cycling performance, but no significant effect of condition for mean RPE or EIP (P > 0.05). In the FP, a ?significant main effect of condition for EIP (F (2, 40) = 4.363, P = 0.019), but no difference for RPE, HR or B[La]. This experiment demonstrated the first time that painful images negatively affect mood and elicit a compassionate hyperalgesia response to exercise. The results demonstrate that an increased pain sensation during exercise (induced via compassional hyperalgesia) can decrease TT performance, and highlights there is an emotional element to the processing of EIP that can be influenced by compassional hyperalgesia. This is probably the consequence of 'top-down' processing increasing the pain sensation elicited by a given 'bottom-up' stimulus. These results highlight the importance of maintaining a positive mood and emotional state prior to and during exercise. The experimental studies performed as part of this thesis provides unique empirical evidence to advance scientific knowledge and understanding of the phenomenon of EIP. This thesis provides further new insights into how different interventions both alleviate and exacerbate EIP, which subsequently influences endurance exercise performance. Furthermore, considering the lack of knowledge regarding the testing and role of EIP in exercise, this thesis contributes to and enhances scientific understanding for how to test for and control these variables

Images depicting human pain increase exercise-induced pain and impair endurance cycling performance

The current study investigated whether viewing images of others in pain influences exercise-induced pain (EIP) and cycling performance. Twenty-one recreational cyclists attended five laboratory visits. The first two visits involved measuring participants’ maximal aerobic capacity and familiarized participants to the fixed power (FP) and 16.1 km cycling time trial (TT) tasks. The FP task required participants to cycle at 70% of their maximal aerobic power for 10-minutes. In the subsequent three visits, participants performed the FP and TT tasks after viewing pleasant, ‎painful or neutral images. Participants rated the subset of painful images as more painful than the pleasant and neutral images; with no difference in the pain ratings of the pleasant and neutral images. In the FP task, EIP ratings were higher following painful compared to pleasant images, while no differences in EIP were observed between any other condition . In the TT, performance did not differ between the pleasant and neutral conditions. However, TT performance was reduced after viewing painful images compared to neutral or pleasant images. HR, B[La], perceived exertion and EIP did not differ between the three conditions. These results suggest that viewing painful images decreases TT performance and increases pain during fixed intensity cycling.

A reduction in maximal incremental exercise test duration 48 h post down hill run is associated with muscle damage derived exercise induced pain

Purpose: To examine whether exercise induced muscle damage (EIMD) and muscle soreness reduce treadmill maximal incremental exercise (MIE) test duration, and true maximal physiological performance as a consequence of exercise induced pain (EIP) and perceived effort. Methods: Fifty (14 female), apparently healthy participants randomly allocated into a control group (CON, n = 10), or experimental group (EXP, n = 40) visited the laboratory a total of six times: visit 1 (familiarization), visit 2 (pre 1), visit 3 (pre 2), visit 4 (intervention), visit 5 (24 h post) and visit 6 (48 h post). Both groups performed identical testing during all visits, except during visit 4, where only EXP performed a 30 min downhill run and CON performed no exercise. During visits 2, 3, and 6 all participants performed MIE, and the following measurements were obtained: time to exhaustion (TTE), EIP, maximal oxygen consumption [Formula: see text], rate of perceived exertion (RPE), maximum heart rate (HRmax), maximum blood lactate (BLamax), and the contribution of pain to terminating the MIE (assessed using a questionnaire). Additionally during visits 1, 2, 3, 5, and 6 the following markers of EIMD were obtained: muscle soreness, maximum voluntary contraction (MVC), voluntary activation (VA), creatine kinase (CK). Results: There were no significant differences (p ≥ 0.32) between any trials for any of the measures obtained during MIE for CON. In EXP, TTE decreased by 34 s (3%), from pre 2 to 48 h post (p < 0.001). There was a significant association between group (EXP, CON) and termination of the MIE due to "pain" during 48 h post (χ2 = 14.7, p = 0.002). Conclusion: EIMD resulted in premature termination of a MIE test (decreased TTE), which was associated with EIP, MVC, and VA. The exact mechanisms responsible for this require further investigation

Development and Initial Validation of the Endurance Sport Self-efficacy Scale (ESSES)

Self-efficacy is likely to be an important psychological construct for endurance sport performance. Research into the role of self-efficacy, however, is limited as there is currently no validated measure of endurance sport self-efficacy. Consequently, the purpose of the present research was to develop and validate the Endurance Sport Self-Efficacy Scale (ESSES). In Study 1, an initial item pool was developed following a review of the literature. These items were then examined for content validity by an expert panel. In Study 2, the resultant 18 items were subjected to exploratory factor analyses. These analyses provided support for a unidimensional scale comprised of 11 items. Study 2 also provided evidence for the ESSES’s convergent validity. In Study 3, using confirmatory factor analyses, further support was found for the 11-item unidimensional structure. Study 3 also provided evidence for the ESSES’s convergent and concurrent validity. The present findings provide initial evidence that the ESSES is a valid and reliable measure of self-efficacy beliefs in endurance sports

The Science of Racing against Opponents: Affordance Competition and the Regulation of Exercise Intensity in Head-to-Head Competition

Athlete–environment interactions are crucial factors in understanding the regulation of exercise intensity in head-to-head competitions. Previously, we have proposed a framework based on the interdependence of perception and action, which allows us to explore athletic behavior in the more complex pacing situations occurring when athletes need to respond to actions of their opponents. In the present perspective we will further explore whether opponents, crucial external factors in competitive sports, could indeed be perceived as social invitations for action. Decisions regarding how to expend energy over the race are based on internal factors such as the physiological/biomechanical capacity of the athlete in relation to external factors such as those presented by opponents. For example: Is the athlete able to overtake competitors, or not? We present several experimental studies that demonstrate that athletes regulate their exercise intensity differently in head-to-head competition compared to time-trial exercises: Relational athlete-environment aspects seem to outweigh benefits of the individual optimal energy distribution. Also, the behavior of the opponents has been shown to influence pacing strategies of competing athletes, again demonstrating the importance of relational athlete–environment aspects in addition to strictly internal factors. An ecological perspective is presented in which opponents are proposed to present social affordances, and decision-making is conceptualized as a resultant of affordance-competition. This approach will provide novel insights in tactical decision-making and pacing behavior in head-to-head competitions. Future research should not only focus on the athlete's internal state, but also try to understand opponents in the context of the social affordances they provide

Transcutaneous electrical nerve stimulation reduces exercise-induced perceived pain and improves endurance exercise performance

Purpose. Muscle pain is a natural consequence of intense and prolonged exercise and has been suggested to be a limiter of performance. Transcutaneous electrical nerve stimulation (TENS) and interferential current (IFC) have been shown to reduce both chronic and acute pain in a variety of conditions. This study sought to ascertain whether TENS and IFC could reduce exercise-induced pain (EIP) and whether this would affect exercise performance. It was hypothesised that TENS and IFC would reduce EIP and result in an improved exercise performance. Methods. In two parts, 18 (Part I) and 22 (Part II) healthy male and female participants completed an isometric contraction of the dominant bicep until exhaustion (Part I) and a 16.1 km cycling time trial as quickly as they could (Part II) whilst receiving TENS, IFC and a SHAM placebo in a repeated measures, randomized cross-over, and placebo controlled design. Perceived EIP was recorded in both tasks using a validated subjective scale. Results. In Part I, TENS significantly reduced perceived EIP (mean reduction of 12%) during the isometric contraction (P = 0.006) and significantly improved participants’ time to exhaustion by a mean of 38% (P = 0.02). In Part II, TENS significantly improved (P = 0.003) participants’ time trial completion time (~2% improvement) through an increased mean power output. Conclusion. These findings demonstrate that TENS can attenuate perceived EIP in a healthy population and that doing so significantly improves endurance performance in both submaximal isometric single limb exercise and whole-body dynamic exercise

Muscle pain induced by hypertonic saline in the knee extensors decreases single-limb isometric time to task failure

Purpose: Increased nociceptive activity and the experience of exercise-induced pain (EIP) may contribute to fatigue during endurance exercise. To investigate this, a pain model that produces pain similar to EIP and decouples its’ relationship to exercise intensity is required. This study 1) compared the quality of pain caused by a hypertonic saline injection into the vastus lateralis in resting and exercise conditions, and 2) investigated whether this pain contributes to changes in time to task failure. Methods: On separate days, eighteen participants completed a time to task failure at 20% maximal voluntary torque (MVT), a resting hypertonic saline intramuscular injection, and in a further three visits a time to task failure at 10% MVT following injection of isotonic saline, hypertonic saline or a control (no injection). Results: In a subset of eligible participants (n = 12), the hypertonic saline combined with 10% MVT produced a qualitative experience of pain (assessed by the McGill Pain Questionnaire) that felt similar to EIP. 10% MVT with hypertonic saline significantly elevated pain intensity in the first 20% of the time to task failure and caused a significantly (P < 0.05) shorter time to task failure (448 ± 240 s) compared with the isotonic saline (605 ± 285 s) and control (514 ± 197 s) conditions. Conclusion: These findings demonstrate that hypertonic saline increases the intensity of pain during exercise, which results in a faster occurrence of exercise-induced fatigue. These results provide important evidence supporting pain as a limiting factor in endurance performance

Endurance performance is influenced by perceptions of pain and temperature: Theory, applications and safety considerations.

Models of endurance performance now recognise input from the brain, including an athlete’s ability to cope with various non-pleasurable perceptions during exercise, such as pain and temperature. Exercise training can reduce perceptions of both pain and temperature over time, partly explaining why athletes generally have a higher pain tolerance, despite a similar pain threshold, compared with active controls. Several strategies with varying efficacy may ameliorate the perceptions of pain (e.g. acetaminophen, transcranial direct current stimulation and transcutaneous electrical stimulation) and temperature (e.g. menthol beverages, topical menthol products and other cooling strategies, especially those targeting the head) during exercise to improve athletic performance. This review describes both the theory and practical applications of these interventions in the endurance sport setting, as well as the potentially harmful health consequences of their use

Tolerance of exercise-induced pain at a fixed rating of perceived exertion predicts time trial cycling performance

To compare the predictive capacity of experimental pain and exercised-induced pain (EIP) on exercise performance. Thirty-two recreationally active male (n = 23) and female (n = 9) participants were recruited. Participants completed measures of pain tolerance by cold pressor test (CPT), pain pressure threshold via algometry (PPT), and EIP tolerance using an RPE clamp trial. A VO2max test provided traditional predictors of performance [VO2max , gas-exchange threshold? (GET), peak power output (PPO)]. Finally, participants completed a 16.1-km cycling time trial (TT). No correlation was found between experimental pain measures (CPT, PPT) and TT performance. However, there was a significant correlation between EIP tolerance and TT performance (R = -0.83, P < 0.01). Regression analysis for pain and physiological predictor variables (mean pain in CPT, PPT, EIP tolerance, VO2max , PPO, GET) revealed that a significant model (P < 0.01) emerged when only PPO (Adjusted R(2)  = 0.739) and EIP tolerance (?R(2)  = 0.075) were used to predict TT performance. These findings suggest that EIP tolerance is an important factor in endurance performance. However, PPT and CPT have limited ability to assess this relationship, and so their use in EIP research should be treated with caution