03/10/2024
Hot off the Press 🔥
The effect of six-week regular stretching exercises on pain sensitivity: an experimental longitudinal study on healthy adults
👉 Background
Current evidence suggests that the main contributor to the effects of stretching exercises are caused by modifications in the subject’s sensation (i.e., stretch, tightness, or pain), resulting in changes in the tolerance to stretch (https://pubmed.ncbi.nlm.nih.gov/8607762/). Stretch tolerance is defined as the capability to tolerate stretch-related discomfort (https://pubmed.ncbi.nlm.nih.gov/19696119/). Previous research indicates that changes in the range of motion following stretching may be a manifestation of altered pain thresholds (https://pubmed.ncbi.nlm.nih.gov/30699073/, https://pubmed.ncbi.nlm.nih.gov/29238214/), suggesting that the tolerance to stretching may be a marker of overall nociceptive sensibility (https://pubmed.ncbi.nlm.nih.gov/34387949/). The increase in stretch tolerance may be contingent on an analgesic effect, allowing for a higher tolerance to passive tension (https://pubmed.ncbi.nlm.nih.gov/30699073/). There may also be a decrease in both regional (e.g., local) and distant (e.g., a remote site of the body) pain thresholds following acute bouts of stretching in healthy adults (https://pubmed.ncbi.nlm.nih.gov/38876646/). Mechanisms such as the modulation of inputs in the spinal dorsal horns (i.e., the Gate Control Theory) (https://meridian.allenpress.com/jcep/article/10/4/150/474534/Effects-of-Acute-and-Chronic-Stretching-on-Pain) and endogenous nociceptive inhibitory mechanisms (https://pubmed.ncbi.nlm.nih.gov/34387949/) have been proposed to be related to the effect of stretching on pain. Previous studies have also found correlations between the relative changes in the range of motion and the relative changes in pressure pain thresholds following stretching (https://pubmed.ncbi.nlm.nih.gov/8607762/, https://pubmed.ncbi.nlm.nih.gov/30699073/, https://pubmed.ncbi.nlm.nih.gov/38876646/).
👉 Stretching exercises are widely used in rehabilitation for pain relief. Although current evidence shows a clinically relevant effect of acute stretching on musculoskeletal (https://meridian.allenpress.com/jcep/article/10/4/150/474534/Effects-of-Acute-and-Chronic-Stretching-on-Pain), neuropathic (https://pubmed.ncbi.nlm.nih.gov/34901069/) and nociplastic pain (https://pubmed.ncbi.nlm.nih.gov/32976664/), there is limited and conflicting knowledge of the effect of regular stretching exercises on regional and widespread pain thresholds (https://pubmed.ncbi.nlm.nih.gov/26032407/, https://pubmed.ncbi.nlm.nih.gov/33367925/).
📘 In this regard, a brand-new study by Støve et al. (2024) explores the impact of a six-week regular stretching regimen on pressure pain thresholds and range of motion (ROM) in healthy adults, and the effects of a four-week cessation period following the intervention. (https://pubmed.ncbi.nlm.nih.gov/39334218/)
👫 Methods
Design: A single-blind longitudinal repeated-measures study.
Participants: 26 healthy adults (mean age: 23.8 ± 2.1 years). Exclusion criteria included cognitive impairments, neurological or musculoskeletal conditions, regular flexibility training, and the use of medications affecting the sensory system.
🧘♂️ Intervention: The intervention comprised six weeks of daily bilateral static stretching of the knee flexors. Stretches were performed either seated on the ground or standing in an alternating fashion. For the seated stretch, the participant sat upright on the floor with one leg straight. The sole of the other foot was placed on the inside of the outstretched leg. The participant leaned slightly forward, trying to touch their toes while maintaining full knee extension. For the standing stretch, the participant placed the heel of the stretching leg on an elevated surface approximately knee to waist high, with the knee fully extended. The participant then flexed forward at the hip. The stretching intensity was standardised by instructing the participants to stretch to the point of discomfort (the sensation of stretch). Each stretch was held for 30 s for two repetitions with a minimum of 30 s of rest between bouts. Adherence was monitored through a mobile health app.
🗜️ Measurements: Mechanical sensitivity was measured using pressure pain thresholds (PPT) at regional (tibialis anterior) and distant (deltoid) sites. Pressure pain threshold (PPT) is defined as the minimum force applied which induces pain. Passive knee extension ROM was also assessed. Measurements were taken at baseline, after six weeks of stretching (post-stretch), and four weeks after cessation (post-cessation).
📊 Results:
🗜️Pressure Pain Thresholds:
✅ There was a 36.7% increase in regional PPT (tibialis anterior) and an 18.7% increase in distant PPT (deltoid) from baseline to post-stretch.
✅ No significant differences were observed between post-stretch and post-cessation, suggesting that the hypoalgesic (pain-reducing) effects persisted even after stopping the stretching exercises. From baseline to post-cessation, a 41.2% increase in distant PPT and a 15.4% increase in regional PPT were observed.
Range of Motion (ROM):
✅ A 3.6% increase in passive knee extension ROM was observed from baseline to post-stretch and post-cessation. The ROM gains were retained after four weeks of cessation, suggesting a lasting effect.
💡 Conclusions:
Six weeks of regular stretching significantly increased both regional and widespread pressure pain thresholds. Moreover, the hypoalgesic effects persisted after cessation, indicating the potential long-term benefits of stretching for managing pain. These supports incorporating stretching into rehabilitation for patients experiencing various types of pain. However, further research is required to explore the long-term effects in clinical populations.
🤔 What do we know about the biological mechanisms?
The present findings align with current evidence suggesting that the hypoalgesic effect of stretching exercises may be related to endogenous inhibitory nociceptive mechanisms (https://pubmed.ncbi.nlm.nih.gov/34387949/, https://pubmed.ncbi.nlm.nih.gov/38876646/). However, emerging evidence indicates that other underlying mechanisms may contribute to the analgesic response following stretching exercises seen in the present study. It has been suggested that stretching exercises may alter sympathetic/parasympathetic balance (https://pubs.sciepub.com/ajssm/2/4/9/), presumably by activating mechanosensory end organs that contribute to sympathetic nervous system inhibition (https://meridian.allenpress.com/jcep/article/10/4/150/474534/Effects-of-Acute-and-Chronic-Stretching-on-Pain). Autonomic dysfunction is regarded as an important factor associated with chronic pain (https://pubmed.ncbi.nlm.nih.gov/25968450/, https://pubmed.ncbi.nlm.nih.gov/27561790/).
❌ Limitations:
The study lacked a control group, limiting the ability to compare the intervention effects against natural time-course or potential learning effects from repeated testing.
Participants were young and healthy, and the results may not apply to older or less active populations.
