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Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy

PainSci » bibliography » Rio et al 2015
Tags: treatment, knee, tendinosis, exercise, chronic pain, sports, strength, rehab, odd, counter-intuitive, good news, leg, limbs, pain problems, overuse injury, injury, self-treatment

One article on PainSci cites Rio 2015: Tennis Elbow Guide

PainSci notes on Rio 2015:

This tiny good news study (of only six athletes, so grain of salt) found that isometric muscle contractions (tensing without moving) “may be used to reduce pain in people with patellar tendinopathy without a reduction in muscle strength.” The pain reduction was substantial and lasted for at least 45 minutes. If this is true of patellar tendinopathy, it’s probably true of others as well … though not necessarily, of course. This was effect was allegedly reproduced by the same researchers (see van Ark 2016, Rio 2017), which got a lot of attention, but a formal replication attempt by another group failed in 2019 (Holden), and British Journal of Sports Medicine expressed concerns about the premature prescription of isometrics (Silbernagel 2019) — about the hype, in other words.

While this is a fascinating and optimistic line of research, the evidence does not make it clear that isometrics are a useful rehab tool for patellar tendinopathy, let alone any other tendinopathy: see Coombes on tennis elbow, Riel on plantar fasciitis, and O’Neill on Achilles tendinitis (all small but negative trials of isometrics).

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

BACKGROUND: Few interventions reduce patellar tendinopathy (PT) pain in the short term. Eccentric exercises are painful and have limited effectiveness during the competitive season. Isometric and isotonic muscle contractions may have an immediate effect on PT pain.

METHODS: This single-blinded, randomised cross-over study compared immediate and 45 min effects following a bout of isometric and isotonic muscle contractions. Outcome measures were PT pain during the single-leg decline squat (SLDS, 0–10), quadriceps strength on maximal voluntary isometric contraction (MVIC), and measures of corticospinal excitability and inhibition. Data were analysed using a split-plot in time-repeated measures analysis of variance (ANOVA).

RESULTS: 6 volleyball players with PT participated. Condition effects were detected with greater pain relief immediately from isometric contractions: isometric contractions reduced SLDS (mean±SD) from 7.0±2.04 to 0.17±0.41, and isotonic contractions reduced SLDS (mean±SD) from 6.33±2.80 to 3.75±3.28 (p<0.001). Isometric contractions released cortical inhibition (ratio mean±SD) from 27.53%±8.30 to 54.95%±5.47, but isotonic contractions had no significant effect on inhibition (pre 30.26±3.89, post 31.92±4.67; p=0.004). Condition by time analysis showed pain reduction was sustained at 45 min postisometric but not isotonic condition (p<0.001). The mean reduction in pain scores postisometric was 6.8/10 compared with 2.6/10 postisotonic. MVIC increased significantly following the isometric condition by 18.7±7.8%, and was significantly higher than baseline (p<0.001) and isotonic condition (p<0.001), and at 45 min (p<0.001).

CONCLUSIONS: A single resistance training bout of isometric contractions reduced tendon pain immediately for at least 45 min postintervention and increased MVIC. The reduction in pain was paralleled by a reduction in cortical inhibition, providing insight into potential mechanisms. Isometric contractions can be completed without pain for people with PT. The clinical implications are that isometric muscle contractions may be used to reduce pain in people with PT without a reduction in muscle strength.

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