Hip adductor strength <80%? You might be 17x more likely to pull your groin
Muscle imbalances. We hear this catch-phrase all the time. Some muscles are too strong and pulling you out of alignment. Other muscles are too weak to stop it from happening. My physio says I’m still weak on a muscle strength test – but I feel like I’m strong enough. Should I keep doing my exercises?
The Scenario: Knees and hips feel good and strong. No previous injuries leading up to this ice hockey game. Half-way through the 1st and I’m feeling pretty warmed-up. Skating hard to catch up with the play when I feel and hear a sudden pop coming from somewhere near my groin. Night’s over. How could this have happened?
Sounds like an adductor strain.
Well, first things first. What are your adductors?
Your hip adductors are a group of 6 muscles comprising the inner compartment of your thigh. The name is derived from the Latin ‘ad’ which means ‘toward’, and thus the name itself describes their collective predominant purpose – to bring one leg closer to the other.
To be able to perform this movement, the majority of them are collectively anchored along the midline of your body along the edge of your pubic bone, which essentially makes up the skeletal framework for your groin. A traumatic pull along any one of these adductors however – like during a sudden push-off maneuver while skating or performing a sustained strenuous heel-hook around an arête – can lead to micro-tearing of the muscle along the pubic bone – aka: the pulled groin.
Why did this happen?
Insufficient warm-up leading to a sudden over-stretch of a cold muscle? Maybe. Poor flexibility leading to micro-tearing of the muscle attachment off the bone? Possibly. Too weak and simply pulling too hard? Could be that too. Your hip adductors were only 80% as strong as your hip abductors? Huh? How would that last theory apply?
What if I told you that if your hip adductor strength was ≤80% of your hip abductor strength that you’d be 17x more likely to experience this groin injury?
What if an assessment was able to reveal this predictive strength deficit earlier – giving you time to improve it to maybe prevent one of the highest recurring sporting injuries from ever happening?
Let’s look at this theory a little closer.
During the NHL seasons spanning 1997 – 1998 and 1998 – 1999, an American physiotherapist from New York named Timothy Tyler and his colleagues set out to investigate whether hip strength ratios (ie. hip strength imbalances) could play a role in the occurrence of a groin strain.1 This study was eventually presented at the annual NHL Team Physicians Meeting in February of 2000 in Toronto, Ontario, and then subsequently published in the American Journal of Sports Medicine in 2001.
In this study – 47 NHL players participated in a pre-season screening exam that examined hip adduction flexibility and hip flexion, hip abduction, and hip adduction strength. During strength assessments, the players were asked to hold specific strength testing positions, and the force required to ‘break’ them out of this position was recorded. The average of 2 maximum efforts for each direction was taken on both legs for every player.
During the 1997 – 1998 and 1998 – 1999 seasons, 11 adductor/groin strains occurred within 8 players (including 1 poor guy who experienced a groin pull on 2 completely separate occasions). The pre-season data from the screening exams were then re-visited to see if anything in the pre-season assessments could have predicted the likelihood of an injury. Here’s what they found:
No difference in hip adduction flexibility between the injured and uninjured players
No difference in hip adduction strength between the injured and uninjured side among the injured players
Injured players had hip adduction strength on average 18% weaker vs uninjured players
Uninjured players demonstrated a hip adduction to abduction strength ratio of 95%
Injured players demonstrated a hip adduction to abduction strength ratio of 78%
Punching out the statistics – the calculations showed that when pre-season hip adduction strength was ≤80% of hip abduction strength, a player was 17x more likely to end up experiencing a groin strain. A pretty powerful stat. And to most of us, 80% probably didn’t even sound that bad. This study also lumped all of the hip adductors into a single category – remember there are 6 of them, and individually their produced actions are slightly nuanced. Is the hip flexed and externally rotated while adducting? Probably more your pectineus. Was it internally rotated instead? Probably more your gracilis. Was it flexed 90 or 60°? Cause that could change it from your adductor brevis to your adductor longus. During physical rehab – it’ll be important to assess the strength of each to ensure you’re not missing it.
Coming back to the scenario though – the vignette isn’t meant to undermine the importance of flexibility/mobility, or the benefit of an adequate warm-up. But what it does highlight is how even good strength in the presence of an imbalance may not be enough. If you feel strong but the ratios still aren’t quite there on re-assessment – as Joel Embiid of the Philadelphia 76ers has popularized – trust the process – and keep working hard, it’ll pay off in the end.
Tyler TF, Nicholas SJ, Campbell RJ, McHugh MP. “The association of hip strength and flexibility with the incidence of adductor muscle strains in professional ice hockey players.” The American Journal of Sports Medicine 2001;29(2):124-128.