Shoulder Impingement in Swimmers
One of the most common injuries that swimmers sustain is to their shoulders. The condition is typically referred to as shoulder impingement and is caused by repetitive pinching of rotator cuff muscles, stroke after stroke after stroke. This pinching leads to microtears, inflammation, and pain. But how does this pinching occur and why doesn't it happen to all swimmers? Well, posture, strength, swim mechanics, and joint mobility affect the position of the shoulder joint during each stroke. Even minor impairments over time can lead to impingement.
Let's start by discussing swimming itself (and for the purpose of this discussion, I will be focusing on freestyle swim stroke). Swimming is actually a closed chain activity, meaning that your hands and arms are working against a force (unlike pitching a ball where the arm is simply moving around through air). Water is 10x denser than air, so swimming requires applying torque, in a coordinated motion against resistance. The amount of load on the shoulder during swimming depends on shoulder position which varies throughout the stroke. We will discuss some of the positions that the shoulder takes while swimming, where problems may occur, and what actions to take to improve and/or prevent impingement.
Repetitive activities like swimming can lead to muscle imbalances over time which can alter movement patterns.
The ligaments on the front aspect of the shoulder (anterior joint capsule) tend to become lengthened or overstretched while the ligaments on the back side of the shoulder joint (posterior joint capsule) tend to tighten. This tissue length imbalance shifts the ball side of the joint slightly forward of socket part of the joint. Now all movement happening is occurring at a joint that is out of alignment. This shift in joint alignment starts the process of impinging the supraspinatus muscle (one of our important rotator cuff muscles and the one most often impinged with swimming). Stretching the posterior capsule and lengthening pec minor muscles can help to place the shoulder joint back into place. It is important to avoid stretching the anterior joint capsule, since it is already hypermobile.
It is important to have adequate shoulder range of motion, primarily flexion, internal and external rotation.
Optimal range of motion for shoulder internal and external rotation is an arc of 180 degree. If internal rotation of the joint is lacking, the scapula (shoulder blade) will tend to protract forward to compensate, but this only encourages impingement so should be avoided. Optimal flexion range of motion is also 180 degrees but this is comprised of movement in both the shoulder joint and the scapula. Only 120 degrees of arm elevation comes from the ball and socket shoulder joint itself, the additional 60 degrees comes from the scapula gliding outward and rotating upwards along the ribcage to help our arms reach 180 degrees overhead. Unfortunately, movement patterns tend to break down at the scapula since it is controlled by the pull of so many different muscles. It is important to make sure that the scapula can coordinate its upward movement to reach overhead, but also retract and rotate posteriorly with stability so that the arm can perform a strong pull through motion during a stroke.
There are 4 phases of the freestyle stroke cycle, each one placing the shoulder in different positions:
This is when the hand enters the water. There is the most pressure on the shoulder due to its position being pushed by the force of water near end range flexion (note: there is only 2 mm of joint subacromial joint space at end range flexion compared to 8-10 mm when the arm is down by your side). The serratus anterior muscle most active during this phase. Some recommendations for decreasing risk of impingement during this phase are to purposely decrease the degree of shoulder flexion at entry. This can be done by rotating the trunk towards your entering arm, opening up that joint space slightly. Have the hand enter with the ring finger. This will encourage a slight external rotation of the shoulder and posterior tilt of the scapula, further decreasing chances of impingement. Allow more upward rotation of the scapula. Lastly, strengthening anterior and middle deltoid muscles can help to resist the upward force of the water, and trapezius, rhomboid and serratus anterior muscles can help to improve scapular stability.
This phase places the most torque on the shoulder, however, because the arm is being pulled downward, there is more joint space available. It is important to place your forearm and hand in the same plane as this will distribute forces along the hand and forearm. Don't allow the hand to cross over the midline of the body since that can increase impingement on the shoulder joint. Pulling the arm in a straight line downwards along the length of your body has been shown to decrease impingement and improve efficiency of the stroke.
The is leaving the water during this phase. Since the hand is down near the hips, there is not much stress on the shoulder and joint space is maximal.
This is where the arm, bent at the elbow is making an arc in the air. Allowing the fingers to relax, and almost drag along the length of the body during that arcing motion encourages external rotation rather than internal rotation during that abduction motion. It is important to rotate the trunk towards the recovering arm. Not only will this place less stress on the shoulder, but it will allow head and neck to rotate less to take a breath. Impingement often occurs on the breathing side of the body, since people tend to extend and rotate their head at the same time. This excessive muscle activity results in decreased scapular posterior tilt and increased scapular elevation. All this, as mentioned before, can contribute to impingement.
Building symmetry in the body is extremely important for avoiding and treating injury. Swimming tends to round the shoulders forward, so it is imperative to strengthen postural muscles on the back side of the body, including the scapula and shoulders. Training to breathe on both sides can further prevent overuse dysfunctional movement patterns. Working with a swimming coach to address swimming form as well as a physical therapist to help balance out muscular weaknesses, joint mobility, and motor patterns will help you to swim with efficiently and injury-free.