Article Review: by Kira Zarzuela, SPT, Tyler Tice, PT, DPT, OCS
Background:
Eccentric exercise is the most commonly prescribed exercise for the treatment of tendinopathy, however, is often too painful to complete. In the competitive season, athletes are less likely to adhere to an eccentric loading program due to increased pain and experiencing either no benefit or worse outcomes, however they may be more compliant with pain reduction strategies that enable ongoing sports participation. Few interventions reduce patellar tendinopathy (PT) pain in the short term. Isotonic exercise has been shown to be as effective as eccentric loading in PT, however there is little to no current research demonstrating this form of exercise’s effect on pain. Isometric exercise has been shown to reduce pressure pain thresholds in normal populations but has not been studied in PT. This study compared the effect of a short bout of isometric and isotonic quadriceps loading on PT pain, maximum contraction strength of the quadriceps, and the neurophysiology of the two exercises.
Methods:
This study looked at six male volleyball players with PT pain. Three players had unilateral pain and the other three had bilateral pain. Immediate and 45-minute effects following a bout of isometric and isotonic muscle contractions were compared. Complete inclusion and exclusion criteria can be found in the original article. Below are the loading protocols utilized in the study.
Outcome measures:
PT pain during the single leg decline squat (SLDS), quadriceps strength on maximal voluntary isometric contraction (MVIC), and measures of corticospinal excitability and inhibition.
Results:
Isometric contractions reduced pain with SLDS from 7.0±2.04 to 0.17±0.41 and isotonic contractions reduced pain with SLDS from 6.33±2.80 to 3.75±3.28.
Isometric contractions released cortical inhibition from 27.53%±8.30 to 54.95%±5.47, but isotonic contractions had no significant effect on inhibition.
Condition by time analysis showed pain reduction was sustained by 45 minutes post-isometric but not isotonic condition.
The mean reduction in pain scores post-isometric was 6.8/10 compared to 2.6/10 post-isotonic
MVIC increased significantly following the isometric condition by 18.7%±7.8, and was significantly higher than baseline and isotonic condition, and at 45 minutes post-intervention.
Discussion:
Isometric exercise immediately reduced patellar tendon pain with the effect sustained for 45 minutes while isotonic exercise had a smaller magnitude immediate effect on patellar tendon pain that was not sustained. There were also no non-responders to isometric exercise regardless of pain severity or length of time of symptoms while there was variable pain reduction experienced following isotonic exercise that was no sustained. Individuals with PT have higher amounts of cortical muscle inhibition for their quadriceps and heavy isometric exercise reduced this inhibition, which may be a factor in the mechanism of pain reduction. The clinic implication of this is isometric exercise may be an important option for clinicians to offer in tendons that are difficult to load without aggravating symptoms. This study had multiple limitations, one of which was the small sample size that was comprised of men, which makes it difficult to determine if the results are generalizable to all patellar tendon pain. Another limitation of the study was participants were diagnosed with patellar tendinopathy so it is difficult to determine if the same effects would be observed in other cases of anterior knee pain. This study also lacked a control group, or group where no intervention was performed, which would further qualify observed results of the study.
Take Home Message:
One of the most well-known interventions for tendinopathy in the world of physical therapy is to eccentrically load the tendon to an individual’s pain tolerance, however what interventions are you left with when the patient is unable to participate because of high levels of pain? The findings from this study give clinicians an alternative intervention for their patients that have more painful tendons by reducing the patient’s pain in the short-term, which would then allow them to tolerate other interventions that may have previously been too painful. As stated in the article, the use of isometric exercise for pain reduction in patellar tendinopathy is a great option for in-season athletes who may not want to stop participating because of their pain but would still benefit from short-term pain reduction. This study had a handful of limitations, such as a small sample size, however this shouldn’t deter clinicians from utilizing isometric exercise as a tool for pain management for PT pain.
Article Reference:
Rio, E., Kidgell, D., Purdam, C., Gaida, J., Moseley, G. L., Pearce, A. J., & Cook, J. (2015). Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. British journal of sports medicine, 49(19), 1277–1283. https://doi.org/10.1136/bjsports-2014-094386