You will probably read, or may have already, multiple articles telling you how to perfect your swim stroke. This is not one of them. Making adjustments to your stroke can certainly help you become more efficient. But, whether you adhere to the paradigms of straight-arm freestyle or front-quadrant swimming, these free-style styles use the same muscles and share similar biomechanics. It’s the same with running. I’ve watched orthopedic experts heatedly debate on whether a heel strike or forefoot strike is most optimal for running, each citing various studies and presenting compelling evidence. But the fact remains, the literature is inconclusive and you are going to run in a way that works for you. Therefore, we’re not going to tell you when your hand should enter the water, or at what angle to hold your elbow when pulling through. Keep doing what you’re doing, but let’s find a way to do it that gives you the best chance for shoulder injury prevention in swimrun so you can enjoy this sport for as long as you can…or at least would like to.
Eighty to 90% percent of your power during freestyle comes from the shoulder (1,2), so it is no wonder that up to 91% of competitive swimmers experience shoulder pain (1,2,3). After combing through recent literature, and cross-referencing that with conferences I’ve attended and my own knowledge and background as a physical therapist, I’ve tried to clearly distill some common shoulder injuries for endurance swimmers and the most evidence-based shoulder injury prevention in swimrun. To make the reading of this less painful than some of the injuries themselves, I’ve made an effort to keep it simple, but have also included source material at the end of this article if you really want to take a deep dive into swimmer’s shoulder pathologies.
Phases of Swimming and Key Muscles
To understand shoulder injury prevention in swimrun, let’s begin with a common language around the phases of swimming. While the phases of swimming can be broken up into five or more segments, I’ve decided to pare it down to four: glide and reach, pull through, hand exit, and recovery. Below shows each of these phases using the left arm as the reference and lists key muscles involved in each phase (3).
Phase 1: Glide and reach, or “catch phase”
- upper trapezius
- serratus anterior
Phase 2: Pull through (early, mid, late)
- pectoralis major
- latissimus dorsi
- serratus anterior
- teres minor
Phase 3: Hand exit or end of pulling
- deltoids (posterior, middle)
Phase 4: Recovery (early, mid, late)
- deltoids (posterior, middle, anterior)
- upper trapezius
- serratus anterior
Imagine your shoulder joint is a like a golf ball on a tee. Ideally, you want the ball snug in the socket without too much extraneous movement. This is what we would call “joint stability”. If the ball is not stable, it will roll around and potentially push up against surrounding structures (muscles, tendons, ligaments) causing impingement, and possibly even tearing those structures, leading to a rotator cuff or labral tear. We call this excessive movement joint hypermobility, or in extreme cases, joint instability. So how does too much movement in the joint happen in the first place?
Muscle Fatigue + Muscle Imbalances = Joint Hypermobility or Instability
Two key muscles used throughout the swim stroke and through the majority of the pull phase are the serratus anterior and subscapularis. These muscles are known for stabilizing the shoulder blade.
The serratus anterior is what I like to call the Bruce Lee punching muscle. Hold your arm straight out 90 degrees in front of you and imagine you are going to deliver Bruce’s famous 1-inch blow. The primary muscle you would use to do that is serratus anterior. This muscle stabilizes and rotates the shoulder blade upward during the glide/reach and pull through phases of swimming (1,4).
The subscapularis (no creative nickname for this one) is the muscle that internally rotates your arm. So, now imagine you were on the receiving end of that 1-inch punch and are now lying flat on your back with your arms out on either side and your elbows bent at 90 degrees (like cactus arms). The muscle required to lift your hand up off the floor while keeping your elbow on the floor in order to flip off the person who just punched you is subscapularis (subscap don’t take no crap). This muscle helps serratus anterior stabilize the shoulder blade, as well as internally rotates the arm during the pull through phase of swimming (1,4).
When these muscles fatigue, the pull of stronger muscles takes over and adversely affects the movement within the shoulder joint.
Shoulder hypermobility or instability
With fatigue of the serratus anterior and subscapularis, combined with muscle imbalances of over strengthened or tight pecs and lats, leading to potential fatigue of the rotator cuff, the shoulder joint becomes unstable. The golf ball is no longer sitting snuggly on the head of the tee, but is rolling around erratically with every swim stroke you take. It is now impinging tendons, placing stress on ligaments, and potentially tearing those structures due to repetitive abnormal joint mechanics. So the next logical question, is how can I prevent this? But first, lets look at some surprising factors that do and do not put you at risk for shoulder pain with swimming.
In a 2015 systematic review, Hill et al. evaluated the evidence for risk factors which may predispose swimmers to shoulder pain or injury. While this review found no high level of evidence supporting any particular risk factor, it did clarify risk factors of a moderate level and low level of certainty. Test your assumptions below regarding what puts you at risk for shoulder pain and injury.
Shoulder Injury Prevention in Swimrun
So, we know with moderate certainty that joint instability, decreased internal range of motion, swimming competitively, and a history of shoulder pain predispose you to experiencing shoulder pain when swimming. Of those four risk factors, two can be modified with exercises: range of motion and joint instability. And we also know some specific causes of joint instability: serratus anterior, subscapularis, and rotator cuff fatigue, as well as, muscle imbalances of the pecs and lats. Therefore, we recommend a few simple exercises that target these risk factors and specific muscle groups to help shoulder injury prevention in swimrun and ensure a long and happy swimrun journey.
References for further reading
- De Martino I, Rodeo S. The swimmer’s shoulder: Multidirectional instability. Curr Rev Musculoskelet Med. 2018;11(2):167-71.
- Matzkin E, et al. Swimmer’s shoulder: Painful shoulder in the competitive swimmer. J Am Acad Orthop Surg. 2016;24(8):527-36.
- Hill L, et al. Risk factors for shoulder pain and injury in swimmers: A critical systematic review. Phys Sports Med. 2015;43(4):412-20.
- Heinlein SA, Cosgarea AJ. Biomechanical considerations in the competitive swimmer’s shoulder. Sports Health. 2010;2(6):519-25.
Disclaimer: The material presented on the Swimrun Labs website is for educational and informational purposes only, and should not be used to replace the diagnosis or treatment provided by a healthcare professional. Please consult a qualified healthcare professional if you are experiencing pain during exercise.