Isometrics Vs isotonics for inseason patellar tendon pain

Hi all,

Welcome to blog number 33! For those in Melbourne here is a link to a free seminar on Hamstring muscle and proximal tendon rehabilitation on 4th Oct 2016.

This weeks blog (subscribe here) focuses on a new RCT by van Ark et al. that compares isometrics vs isotonic rehab for in-season athletes with patellar tendon pain. Previous studies have shown that inseason rehab for this cohort is not really all that successful. This study adds to the literature, but also brings up lots of really interesting questions...

Do isometric and isotonic exercise programs reduce pain in athletes with patellar tendinopathy in-season? A randomised clinical trial

Background: This new RCT is from the group (ie Rio, Cook, etc) that really popularized isometric loading, which has definitely changed the way we rehab tendons. Most people would have seen the Rio et al 2015 study showing that isometrics loading had a greater immediate (they looked up to 45minutes) effect on pain and motor cortex inhibition compared with isotonic loading. They hypothesized that based on this prior study, isometrics would be superior to isotonics for managing patellar tendon pain among inseason athletes.

In the authors' own words: “The aim of this study was to examine whether isometric and isotonic exercises relieve pain in competing athletes with patellar tendinopathy. It was hypothesised that both isometric and isotonic exercises would decrease pain in athletes with patellar tendinopathy in-season and that isometric exercises would decrease patellar tendon pain more than isotonic” exercises.

What they did: They randomized 18-32 year old active basketball and volleyball players into 2 groups: 1=isometrics where on a leg extension at 60 degrees flexion for 45secx5 and at 80%MVC and 2=isotonic was 4 sets of 8 repetitions of 3 sec concentric and 4 sec eccentric phase at 80% of 8RM. Each group performed the exercises 4x/week for 4 weeks. The interventions where matched for time under tension and rest time. Both legs were exercised. Participants did one, then the other, then rested for a further 15 seconds, then went back to the first leg. Participants in the isotonic group were provided with an audio file counting the timing of the exercise.

The primary outcome was numerical rating scale pain on the single leg decline squat with a minimal important clinical difference (MICD) of 2 points. The VISAP was also measured and the MICD was 13. These outcomes were repeated at 4 weeks. At follow up participants also completed an exercise diary and were asked about global improvement.

What they found: 13 participants were randomised to the isometric and 16 to the isotonic group. There were no group differences at baseline for characteristics such as age, gender, duration of symptoms, BMI. Adherence (ie completed exercise sessions) was 81% on average between the groups. Main findings were that pain on single leg decline squat testing, and pain/function on VISA improved in BOTH groups and there was NO significant difference between groups. Group changes were beyond the clinically important cut off for the single leg decline squat measure (about 2.5-3 points) but not in VISA (about 9 points).

Interpretation: The main finding is people with patellar tendinopathy can improve pain and even perhaps function based on VISA when performing an exercise program in season. This is an advancement of the current literature where eccentric loading in season has been shown to have no effect on patellar tendon pain, and can even make some people worse (Visnes et al. 2005).

The author hypothesized that the isometrics would be superior due to the reported superior short term effects on pain and motor cortex inhibition (only based on 1 study). Maybe the study was underpowered to show a difference between the groups (post hoc power not reported) but I don’t think so as mean change in single leg decline squat and VISA were very similar between the groups.

The data seem to support the mantra that ‘load is positive, regardless of the type of load’…with a caveat: as long as it is not provocative. Seems silly to suggest the last bit, ‘as long as it is not provocative’, but not too long ago people were trying to provoke pain with eccentric loading, which is probably why inseason studies like the Visnes study did not work.

For me, what this study really highlights is that we need to learn much more about the long term clinical benefits of isometrics, and that we can’t extrapolate short term to long term effects. Not to say isometrics are not useful, but we need sound reasoning to use them. I go with 2 criteria ie 1 = there is nothing else the person can without flaring their symptoms; and 2 = they offer significant short term pain response that allows better quality of subsequent rehab/training. Simple! Be guided by the individual rather.

So if this mantra of load is positive is true, why is it true? And is it the load or something else having an effect? The authors discuss potential neuromuscular mechanisms, but also rightly say the mechanisms are really unknown. It could be that there are psychological effects at play such as reduced fear, increased self efficacy. Or maybe alot of the positive outcome is explained by context and maybe doing anything may have had the same effect (would the positive effect have been similar if we got them to wiggle their little finger 10 times per day, as long as they really believed that this would have a positive impact?). I don’t think so, but the point is in this study, and many exercise trials, the effect of context and placebo are not controlled.

Some other minor points about the study. Participants exercises at 80% of MVC (maximal voluntary contraction) for the isometric group, and 80% of 8RM for the isotonic group. I wonder whether the last figure is an error? Because 80% of 8RM is probably more like 64% of 1 RM, so not really close to 80% of MVC. There is also no mention of whether participants continued to train/play their basketball and volleyball at the same level during the interventions. Once possibility may be that they reduced their loads and this could explain the change in pain over the 4 weeks.

Overall, a great study, and trials are always hard to carry out so well done to the authors. The study adds to our repertoire of inseason options for rehab and I love it because it reinforces my bias: load them gradually, and as long as the load is not provocative, then it will probably do them some good!

See you next time

Peter