Swimmer's Knee: Causes and Rehabilitation of Breaststroker's Knee (Medial Collateral Ligament)

Introduction

Breaststroke is the most widely learned stroke in Taiwan, chosen by middle-aged and older swimmers for its gentle, unhurried rhythm, and by beginners for its more manageable breathing pattern. Its popularity is evident at swimming pools across the island. However, breaststroke carries a notorious “side effect”: Breaststroker’s Knee.

This injury primarily affects the medial collateral ligament (MCL) of the knee and its surrounding structures. It results from repeated valgus stress caused by the whip kick unique to breaststroke, and it is the most common sports injury among competitive breaststroke swimmers, with an incidence rate as high as 73%. Even recreational swimmers are not immune if they maintain poor form over the long term.

Causes of Breaststroker’s Knee: An Anatomical Analysis

The breaststroke kick can be broken down into three phases: “knee tuck → knee external rotation (outward turn) → whip extension.” The problem arises during the whip (extension) phase: as the lower legs sweep outward and then snap rapidly back together, the knee joint is subjected to valgus stress, which directly stretches the MCL.

The following factors increase the risk of breaststroker’s knee:

• Excessive kick width: when the ankle opening angle exceeds 60°, valgus stress roughly doubles
• Snapping the legs together before the knee is fully extended: the ligament is repeatedly loaded under uneven stress
• Weak gluteus medius: insufficient hip abduction control causes the knee to compensate with more lateral load
• Insufficient ankle dorsiflexion: limited ankle mobility forces the knee to compensate with external rotation
• Sharp increase in training volume: a large jump in distance or intensity over a short period

Injured Structures and Symptoms

Diagnosis and Self-Assessment

The following manual tests can help with preliminary identification:

• Valgus Stress Test: with the knee extended, pressure is applied from the outside inward; pain or laxity on the inner knee suggests MCL injury
• Thessaly Test: standing on one leg with the knee bent about 20°, rotate the body toward the affected side; pain on the inner knee suggests a meniscus problem
• Breaststroke-Specific Test: perform the breaststroke kicking motion in water or on land; pain appearing on the inner knee is a warning sign

If a ligament tear or meniscus tear is suspected, an orthopedic diagnosis and MRI confirmation should be arranged.

Phased Rehabilitation Plan

Acute Phase (Days 1–3 After Injury)

• Follow the RICE principle: Rest, Ice (20 minutes, 3–4 times daily), Compression (elastic bandage), Elevation
• Suspend all breaststroke training; backstroke or flutter-kick with a kickboard (freestyle kick) can be used instead
• NSAIDs (non-steroidal anti-inflammatory drugs) may be used as directed by a physician

Subacute Phase (Weeks 2–4)

• Isometric strengthening: sitting with a pillow slightly bending the knee, press down firmly or push outward (without moving) to strengthen the quadriceps and hip abductors
• Straight Leg Raise (SLR): lying on your back, slowly lift the affected leg straight to 30–45° to strengthen the quadriceps
• Gluteus medius strengthening: side-lying leg abduction and resistance-band clamshells, 15 reps × 3 sets per side
• Proprioception training: progress from double-leg stance to single-leg stance, then to unstable surfaces

Return-to-Swimming Phase (Weeks 4–8)

• Maintain aerobic fitness first with kickboard plus freestyle flutter kick
• Gradually introduce breaststroke technique correction: narrow the kick width and ensure the knee is fully extended before the whip
• Use swim fins (short-blade fins) to assist and reduce lateral knee stress on each kick
• Start breaststroke distance at 200 meters, increasing by no more than 10% per week

Practical Recommendations

1. Correcting breaststroke technique is the most important measure for preventing recurrence: find an experienced coach to analyze underwater video
2. Major hospitals across Taiwan have sports injury specialists in their rehabilitation departments — do not delay seeking treatment. Early-stage MCL injuries can typically return to training within 4–6 weeks
3. For long-term protection, wearing a knee brace (MCL support type) during high-volume training weeks can reduce lateral stress
4. If you are over 45 years old and swim breaststroke regularly, schedule an annual knee ultrasound to catch cartilage wear early
5. If you notice mild knee swelling after swimming, ice it immediately for 10 minutes and consider stopping breaststroke for the day

Conclusion

Breaststroker’s knee is a preventable sports injury, and the key lies in correct technique and progressive training. Don’t give up swimming entirely because of pain — instead, work with your coach and medical team to adjust your form and strengthen your supporting muscles, so that breaststroke can continue to play an important role in your healthy, active life.

Related Reading

• Swimmer’s Knee: Causes, Prevention, and Rehabilitation of Breaststroker’s Knee
• Breaststroker’s Knee: Medial Collateral Ligament Stress Caused by the Whip Kick
• Swimmer’s Knee: A Complete Guide to Breaststroke Knee Injuries
• The Outsweep and Insweep of Breaststroke: Balancing Knee Protection and Propulsive Power