BACKGROUND: Shoulder girdle pain is a common disabling complaint with a high lifetime prevalence. Interventions aimed at decreasing shoulder pain without stressing shoulder girdle structures have the potential to improve participation in multimodal shoulder rehabilitation programs. HYPOTHESIS/PURPOSE: The aim of this study was to determine the acute effects of moderate intensity lower extremity exercise on mechanically induced shoulder pain in individuals without shoulder injury. It was hypothesized that participants would exhibit less shoulder pain, as indicated by increased pain thresholds, following lower extremity exercise. STUDY DESIGN: Repeated measures study. METHODS: Thirty (30) healthy participants were recruited to participate in this study. Pain pressure algometry was used to mechanically induce shoulder pain over the infraspinatus muscle belly. This was performed on the dominant shoulder before and immediately after performing 10 minutes of moderate intensity lower extremity exercise using a recumbent exercise machine. Heart rate and rate of perceived exertion were measured following exercise. Repeated measures ANOVA was used to compare pain pressure threshold scores between the baseline and post-exercise time points. Significance was set at p ≤ 0.05 . Effect size (ES) was calculated using Glass's Δ. RESULTS: Moderate intensity lower extremity aerobic exercise led to significantly (F = 8.471, p = 0.003) decreased evoked shoulder pain in healthy adults with moderate effect sizes (0.30-0.43). CONCLUSIONS: Lower extremity aerobic exercise significantly decreased pain of the infraspinatus in this sample of young healthy participants. Utilization of lower extremity exercise may be of benefit for younger patients to decreased acute shoulder pain. LEVEL OF EVIDENCE: 2b: individual cohort study.

A significant driver of pain in low back pain (LBP) is alteration to endogenous pain modulation (EPM). EPM can be measured using quantitative sensory tests (QST), which provides important information on nociceptive pathways. Exercise therapy is recommended as the first line of care for LBP; however, there is limited information on the mechanisms of action that lead to symptom improvements. The first manuscript was a scoping review that summarized protocols used to assess EPM using QST such as pain pressure threshold (PPT), temporal summation (TS), conditioned pain modulation (CPM) or exercise-induced hypoalgesia (EIH) in LBP. Scientific databases were searched for articles that used QST or EIH protocols in LBP. In total, 193 studies were included in this review: 172 used PPT, 54 used TS and 53 used CPM and 5 investigated EIH. There was high variability in the type of equipment, timing, trials, and testing location with many studies not reporting this information. The results demonstrate a need for standardized protocols and reporting guidelines as well as further research to aid in selecting the most appropriate QST parameters for different clinical presentations. The second manuscript was a pilot study that assessed the feasibility of a protocol investigating if changes in EPM occur after exercise therapy. Participants were recruited through a larger trial (WELBack) and were randomized to receive one of two exercise therapies. Participants attended two testing sessions (before and after an 8-week treatment) consisting of PPT, TS, CPM and EIH. Thirty-six participants were recruited and completed baseline assessments. In total, 32 (88.9%) participants completed the follow-up assessment. The results demonstrated that the protocol was feasible. Improvements to patient reported outcomes were seen, but not to all EPM measures. Future work should consider changes to the CPM protocol, and a fully powered study to investigate EPM changes after exercise therapy. / Thesis / Master of Health Sciences (MSc) / Low back pain (LBP) may occur because of changes in our nervous system, rather than a physical injury. However, there is no previous research on if exercise can improve these changes. The purpose of this thesis was to develop and test a protocol to assess how the body processes pain, and if this can change after exercise. We summarized past research on how four tests to assess pain processing have been performed. The results showed many differences in how these tests were performed and reported. More consistency and guidelines are needed to improve how these tests are conducted. Next, we conducted a study aimed to assess the feasibility of a protocol to see if changes occur in how the body processes pain after an exercise therapy program. The results of this study showed the protocol was feasible, and trends in improvement on some but not all measures.

This study assessed the effect of an eight-minute cycling intervention using varying intensities on exercise-induced hypoalgesia (EIH). Generally, current research examines EIH using protocols that last for more than 10 minutes and reach 75% of an individual's VO2 peak. The main objective of this study was to examine the effect of varying intensities on pressure pain threshold (PPT) and heat pain threshold (HPT) at the thigh and forearm, tested pre- and post-cycling intervention. Healthy male participants (n=16) performed a graded exercise test on a cycle ergometer to establish their peak power output (PPO). In subsequent visits, participants completed five different 8-minute cycling interventions, with intensities randomly assigned to one of three counterbalanced orders. HPT and PPT were applied to the thigh and forearm two times before and after each cycling intervention. Additionally, there was a notable effect of intensity on PPT in the thigh, with significant changes at intensities of 90% (p = 0.024) and 100% (p = 0.003). In the forearm, repeated measures ANOVA indicated that there was no significant interaction or main effect for intensity and time. Similarly, for HPT, the analysis did not show significant interaction or main effects for both intensity and location. This study was the first to examine EIH using an 8-minute cycling intervention on a cycling ergometer at individualized intensities. Higher intensity cycling sessions generated EIH locally in the thigh using PPT. This intervention appeared to target the nociceptors activated by mechanical, rather than thermal stimuli, further highlighting the multi-faceted nature of EIH. A short but high intensity cycling intervention may have clinical relevance, as it can provide an intervention to reduce localized pain immediately after exercise using a pressure pain stimulus.

Exercise-induced hypoalgesia (EIH) is the reduction in pain sensitivity following exercise. High-intensity or prolonged exercise is typically required to elicit an EIH response, but there is limited evidence suggesting that low-load resistance exercise with blood flow restriction (LL+BFR) may be able to elicit a robust EIH response. The purpose of these investigations was to assess the magnitude, duration, and proposed mechanisms of EIH following LL+BFR, LL with normobaric systemic hypoxemia, BFR only without exercise, high-load exercise, and a control intervention. The first study evaluated local and systemic pain pressure threshold and tolerance responses one-hour post-exercise. The results indicated that LL+BFR induced similar EIH responses to high-load resistance exercise 0- and 15-minutes post-exercise but only LL+BFR elicited an EIH response present 60-minutes post-exercise. The second study evaluated neuromuscular and perceptual responses, both proposed EIH mechanisms, during exercise. Similar neuromuscular responses were observed in all interventions. Participants reported higher ratings of perceived exertion during LL+BFR and high-load exercise, and higher levels of perceived pain during LL+BFR. These results suggested that despite high levels of motor unit recruitment, there were divergent EIH responses. However, increased pain during exercise may be a mediating factor of EIH after resistance exercise. The third study evaluated peripheral and central cardiovascular responses, which have also been hypothesized to mediate EIH. LL+BFR resulted in greater increases in systolic blood pressure during the first set of exercise, and diastolic blood pressure during all sets of exercise. LL+BFR and BFR only attenuated changes in heart rate variability (HRV). LL+BFR induced the largest increase in deoxyhemoglobin and total hemoglobin and lowered tissue saturation index. BFR only progressively increased oxyhemoglobin and total hemoglobin levels. The local and systemic cardiovascular responses suggested that prolonged EIH following LL+BFR could be related to increased central or peripheral cardiovascular stress.

Exercise-induced hypoalgesia (EIH) denotes the phenomenon wherein physical activity induces a diminished sensitivity to pain, holding significant implications for pain management modalities. This investigation sought to evaluate the reproducibility of pressure pain thresholds (PPT) subsequent to dynamic resistance exercise and juxtapose PPT measurements during periods of quiet rest against those immediately post-exercise. A cohort of five healthy participants underwent three separate sessions, wherein PPT assessments were conducted pre- and post-exercise. Findings revealed a nuanced reliability in PPT measures during EIH evaluation, necessitating judicious interpretation due to the constrained sample size. Comparative analyses with antecedent research underscored discernible disparities in exercise intensities and methodological approaches, accentuating the imperative of considering idiosyncratic responses and procedural distinctions. Despite inherent limitations, notably the modest sample size, this inquiry furnishes valuable insights into the intricacies of EIH assessment, elucidating the complexities inherent in advancing knowledge within the domain of pain modulation research. Prospective investigations with larger and more heterogeneous cohorts are imperative to fortify the dependability and generalizability of findings in this realm.

Introduktion: En minskad smärtkänslighet som uppkommer under eller efter träning är ett fenomen som kallas för träningsinducerad hypoalgesi (Exercise-induced hypoalgesia, EIH). Metodiken för studier om EIH är mångsidig och resultaten har därför inte alltid varit samstämmiga. Aerob träning har visat sig kunna höja smärttröskeln och minska smärtkänsligheten hos individer. Forskningen om aerob kapacitet och dess samband med EIH hos friska individer är bristfällig.  Syfte: Att undersöka effekten av ett aerobt träningspass på smärtkänslighet samt att analysera sambandet mellan aerob kapacitet och smärtkänslighet hos friska individer.  Metod: Ett submaximalt cykeltest utfördes av 19 friska individer mellan 20-38 år, i syfte att estimera maximal syreupptagningsförmåga (VO2max). Detta var följt av ett EIH-test för att undersöka eventuell höjning av trycksmärttröskeln (Pressure pain threshold, PPT). EIH-testet bestod av ett 15 minuters cykelpass på 75% av VO2max där mätning av PPT utfördes på arbetande (ben) respektive vilande (arm) muskulatur, direkt före och direkt efter träningspasset.   Resultat: En signifikant ökning av PPT för arbetande muskulatur (p=0,018) påvisades efter träning. Ingen signifikant förändring av PPT påvisades för vilande muskulatur (p=0,052). Det observerades inget signifikant samband mellan maximal syreupptagningsförmåga (VO2max) och EIH-effekt (ben, p= 0,860; arm, p= 0,942).  Konklusion: Ett högintensivt aerobt cykelpass gav en signifikant höjning av PPT för den arbetande muskulaturen. Inget signifikant samband påvisades mellan VO2max och EIH-effekt (differensen mellan PPT direkt efter och direkt före träning). Ytterligare studier med ett högre deltagarantal behövs för att undersöka detta samband mer ingående samt för att underlätta jämförelser mellan studier.