The primary goal of this study is to test whether 12 weeks of progressive resistance exercise is an effective non-pharmacological treatment for reducing pain in people with multiple sclerosis and chronic pain.

The study will be a randomized controlled trial with multiple training sites. After baseline testing, participants will be randomly assigned to either a 12-week progressive resistance exercise intervention followed by a 12-week follow-up period or to a 24-week waitlist control group that receives usual care.

It is hypothesized that people with multiple sclerosis and chronic pain who receive the intervention will experience greater reductions in pain (i.e., clinically relevant reductions) compared to the waitlist control group (primary hypothesis), and that this pain reduction will be preserved after a 12-week follow-up period (secondary hypothesis).

Purpose and Hypotheses:

The main purpose of this project is to understand the impact of pain in people with multiple sclerosis, how exercise may affect pain symptoms, and whether these effects depend on the underlying pain mechanisms and/or biopsychosocial factors.

The purpose of the main study (study 2) is to test the hypotheses that:

People with MS receiving 12 weeks of resistance exercise will experience superior average analgesic effects (i.e., clinically relevant reductions), compared with MS controls receiving usual care (primary hypothesis), and this analgesic effect will be preserved after a 12-week follow-up period (secondary hypothesis).

The purpose of studies 1,3, 4, and 5 is to test the hypotheses that:

• In people with MS, pain severity will be negatively associated with physical activity, everyday life, walking ability, sleep quality, and/or quality of life, while being positively associated with anxiety, depression, and/or fatigue (study 1).
• People with MS suffering from mixed type pain will experience greater analgesic effects after 12 weeks of resistance exercise compared to people with MS suffering from neuropathic pain (study 3).
• A single bout of resistance and aerobic exercise will acutely induce an analgesic effect as well as a reduction in pain sensitivity immediately after an exercise session, compared with pre-exercise levels, transiently disappearing over the next 15 minutes (study 4).
• Our multifactorial model, incorporating biomarkers, sensory profiles, pain phenotypes, and patient-reported outcomes, is hypothesized to explain the variability of the analgesic effects of resistance exercise to a large extent (i.e., approximately 81%1)(study 5).

Background:

Multiple sclerosis (MS) is a chronic neurodegenerative demyelinating disorder of the central nervous system with profound physical, cognitive, and social consequences. Symptomatic treatment to address these consequences and to improve the quality of life in people with multiple sclerosis (pwMS) is thus essential. One symptom that significantly affects the quality of life in pwMS is pain. Pain is one of the most common symptoms in MS and has recently been estimated to affect as many as 75% of all pwMS. The International Association for the Study of Pain (IASP) has proposed three mechanistic descriptors that may identify different primary pain types or mechanisms, which may exist alone or in combination (i.e., mixed-type pain): 1) Neuropathic pain, defined as pain caused by lesions or disease of the somatosensory nervous system 2) Nociceptive pain, defined as an appropriate pain arising from the activation of nociceptors in non-neural tissue. 3) Nociplastic pain, defined as the presence of pain despite any apparent damage to neuronal or non-neuronal tissue. It is not possible to exclude neuropathic pain in MS, considering the neurodegenerative nature of the disease. However, it may not be the only/or dominant descriptor underlying the experienced pain. Thus, pain will henceforth be referred to as either neuropathic or mixed in the current project.

The majority of current analgesic (pain relieving) treatments include pharmacology and account for approximately 30% of the total medication in MS 7. Pain medication is known to be costly and has extensive adverse effects. Thus, cost-effective non-pharmacological analgesic treatment options without substantial side effects are highly warranted in MS.

Exercise might be exactly such an option. In the general population, exercise has been shown to improve pain symptoms, be cost-effective, and present few, if any, adverse effects beyond exercise-induced soreness. Exercise has been observed to have both acute and chronic beneficial effects on perceived pain in other populations. In neurodegenerative populations, only limited evidence exists, but analgesic effects of exercise have been reported in Parkinson's Disease. A systematic review in 2019 identified 10 exercise studies that had pain as an outcome, which overall suggested a chronic analgesic effect of exercise In MS. However, across these 10 exercise studies, pain was assessed as a secondary outcome, and participants were not recruited based on their initial baseline pain status (i.e., some participants did not experience pain symptoms at study entry).

An important distinction relates to the potential different acute and chronic analgesic effects obtained following different exercise modalities. In other populations, evidence points to resistance exercise as one of the most potent modalities in terms of achieving analgesic effects, although verifying studies in MS are lacking. Examining the efficacy of basic exercise modalities, such as resistance exercise, while further elucidating underlying mechanisms, appears highly relevant in order to improve pain management in people with MS.

In the majority of treatments, a response heterogeneity has been observed, and this also seems to be the case for analgesic treatments. Studies based on surgical and pharmacological treatments of pain have had success identifying that different pain biomarkers, such as inflammatory biomarkers, sensory profiles, and patient-reported outcomes, can predict the analgesic effects in patients. Additionally, we have seen that combining different pain biomarkers yields a larger predictive value than only assessing a single pain biomarker with a study showing such models to explain up to 81% of the variability of clinical pain intesity. However, such predictive models have not yet been adopted in any exercise treatments. Exploring how analgesic effects induced by resistance exercise are associated with - or can even be predicted by - relevant factors appears highly relevant to facilitate and prescribe personalized pain treatment.

In summary, research investigating whether exercise holds the potential to induce analgesic effects in people with MS affected by pain, both in the long-term (i.e., the pain level after a period of regular exercise sessions) and/or acutely (i.e., effects observed immediately after a single exercise session), is highly warranted. Furthermore, insights into underlying characteristics and how they affect the analgesic potential of resistance exercise are necessary to optimize personalized treatment prescription in MS.

Methods:

Study Design To expand our current understanding of the effects of exercise on pain in MS, we have designed a assessor blinded randomized controlled trial (RCT) with follow-up (study 2) with four integrated sub-studies: an initial cross-sectional study (study 1), an exploratory interventional study (study 3) an acute interventional study (study 4) and yet an exploratory interventional study (study 5) (see figure Patient and public involvement

Study 1: This is a cross-sectional survey-based study (i.e., relying on self-reporting) using Redcap, investigating the association between pain severity (NRS0-10 ≥3 ) and physical activity, walking ability, sleep quality, anxiety and depression, fatigue, as well as quality of life. This includes a comparison between people with MS having severe pain (NRS0-10 ≥3) and having no (NRS0-10 = 0) mild pain (NRS0-10 <3). Furthermore, this study will serve as a screening tool for study 2.

Study 2: ("the main study"): Upon interest and fulfillment of eligibility criteria, potential participants identified via study 1 with pain levels NRS0-10 ≥3 will be enrolled and randomized to either 12 weeks of progressive resistance exercise, succeeded by a 12-week follow-up period, or to a 24-week waitlist control group. During the follow-up period, participants will be encouraged to continue exercising independently and will be asked to keep an exercise diary. The control group will proceed with their habitual lifestyle during the 24 weeks.

Study 3: Participants from the waitlist control group in study 2 will, after 24 weeks, be enrolled into the same 12-week intervention as provided in study 2. The control group data derived from weeks 24 to 36 will be pooled with data from the intervention group in study 2, enabling an exploratory analysis of potential phenotype-dependent differences in the analgesic effect of exercise on pain. This design will furthermore ensure that all participants are enrolled in an exercise intervention (either from weeks 0-12 or 24-36), which is likely to promote study adherence.

Study 4: To determine the acute effects of exercise on pain, data on pressure pain threshold (PPT) and pain severity (NRS0-10) will be extracted immediately before and after a bout of resistance exercise during studies 2 and 3. Furthermore, pain severity will be monitored at 5-, 10-, and 30-minute post-exercise. To investigate any potential modality-dependent variations in the acute effects of exercise on pain, the described protocol will be further applied to a 45-minute bout of aerobic exercise. Moreover, measurements of PPT and pain severity will be applied to a bout of isometric exercise at baseline, post-assessment, and at follow-up to assess potential changes in the acute pain response to exercise following 12 weeks of resistance exercise.

Study 5: To evaluate the predictive value of a multi-factorial approach on the effect of exercise on pain, blood samples, sensory profiles, and patient-reported outcome measures (PROMs) will be collected at baseline and after interventions in both groups (i.e., T0 + T12 for the intervention group and T24 + T36 for the wait-list group).

Interventions:

All of the following interventions will be supervised and tailored to the individual participant´s absolute strength, ensuring equal relative intensity throughout the project.

Main intervention - Progressive resistance exercise (Chronic effect) Description and progression Load (RM): 15 (week 1-3), 12 (week 4-6), 10 (week 7-9), 8 (week 10-12) Number of repetitions: 12 (week 1-3), 10-12 (week 4-6), 8-10 (week 7-9), 6-8 (week 10-12) Number of sets: 3 (week 1-6), 4 (week 7-12) Contraction type: Isotonic (concentric and eccentric) Recovery time between sessions (hours): >48

Progressive resistance exercise (Acute effect) At session 2 during week 1, participants will undergo the aforementioned resistance exercise regimen consisting of 12 repetitions of 15 RM for 3 sets, interspersed by 2-3 minutes.

Aerobic exercise (Acute effect) At training session 4 during week 2, participants will undergo a separate bout of aerobic exercise consisting of 30 minutes at 75% - 80% of estimated HRmax, using a bicycle ergometer. The session will commence with a 5-minute warm-up and terminate with a 5-minute cool-down using the same bicycle ergometer.

Isometric Exercise (Acute effect) To determine the acute pain response to exercise and assess potential changes following 12 weeks of resistance exercise, participants will undergo a single bout of isometric exercise of the lower extremities using a leg press dynamometer at an intensity of 30% of maximal voluntary contraction for 90 seconds at baseline and post-intervention (T0+T12 or T24+T36).

Outcomes:

See section "Outcome Measures" for specifications. Additionally, contact information, demographic information, health and medication information as well as blood samples will be obtained.

Statistical considerations:

To assess differences between participants experiencing moderate to severe pain and participants experiencing mild to no pain with regard to selected parameters, a linear mixed model will be applied in study 1. To analyse the effects of exercise on pain severity (chronic and acute), and potential phenotype-dependent differences, a linear mixed-effects intention-to-treat model (including all participants enrolled at baseline) will be applied to study 2, 3, and 4. Finally, to describe the chronic postinterventional pain severity in study 5, a supervised multivariate data analysis with "Data Integration Analysis for Biomarker Discovery" using Latent Components (DIABLO) will be applied.

The main study (study 2) will be powered based on the primary outcome measure NRS0-10, relying on data from previous exercise studies in MS and other relevant populations24,52-54. A two-sample two-sided power calculation resulted in a total of n=58 subjects, which will be expected to be enrolled in each group (α=0.05; power=0.9; control pre-post change 0.3 NRS0-10 score and SD=1.8; exercise pre-post change 1.2 NRS0-10 score and SD=1.8; dropout rate=15%). Hence, a total of 116 participants will be enrolled in the present study.

Randomization:

After baseline assessment of participants, they will be randomized to either the intervention or waitlist control group using a 1:1 ratio. A computer-generated list of random numbers will be conducted in the Research Electronic Data Capture (REDCap) system. The randomization will be stratified by site and will be blinded to outcome assessors.

Perspectives:

The findings of this project have the potential to establish progressive resistance exercise as an effective, safe, and accessible treatment of pain in people with MS and elucidate how this effect may be distinct depending on pain phenotype, inflammatory biomarkers, as well as psychological and physical states. Furthermore, it will examine the acute effects of resistance and aerobic exercise on pain, thereby advancing the understanding of their interrelationship in this population. Finally, insights into the impact of pain in MS will highlight key considerations for pain management. Conclusively, this study has the potential to transform pain management for people with MS suffering from pain worldwide by reducing reliance on pharmacological analgesics and, as a result, minimizing associated adverse effects and lowering societal costs.

Inclusion criteria: Average pain levels of >3 on the Numerical Rating Scale from 0-10 (NRS0-10), age ≥ 18 years, a valid MS diagnosis (ICD-10 code: G35), ability to self-transport to test and exercise.

Exclusion Criteria: Pregnancy, Diabetes, neurological or other comorbidities that hinder participation in the study, relapse within the past 2 months, classified as high cardiovascular risk according to the American College of Sports Medicine´s guidelines, and participation in structured exercise over the past 3 months (≥ 2 sessions/week).

Prior to analysis, pseudonymized whole blood and plasma samples will be shipped by project personnel to Aalborg University, Selma Lagerløfs Vej 249 and stored in a locked -70°C freezer until they are analyzed, ensuring sample integrity and minimizing technical bias. miRNA analysis will be carried out by QIAGEN Genome Service, located in Hilden, Germany. For this purpose, 200/400 ul per sample, completely anonymized, will be shipped in cryo boxes from Aalborg University to QIAGEN in Hilden, Germany.

Analysis of 96 Inflammatory biomarkers will be performed by BioXpedia A/S, Palle Juul-Jensens Blvd. 82, 8200 Aarhus N, or carried out by Associate Professor Rocco Giordano at Aalborg University, SUND, Selma Lagerløfs Vej 249. All of the abovementioned analyses will be run following and respecting GDPR related laws.

Data on pain distribution will be shared with Navigate Pain (Aglance Solutions) and stored on Europe-based servers complying with GDPR.

Sharing of data will commence February 2026 and is expected to terminate within a 5-year period following August 2028.

Data will be accessible exclusively to authorized personnel on encrypted servers. Data collection and data management will be conducted solely by trained staff operating under restricted access privileges.