Side Stitch and Pacing in a School 1500 m Runner
A 16-year-old girl training for the school 1500 m race runs at a pace of 4 min 10 s per km. At 800 m she feels a sharp pain under her right rib cage, her breathing becomes shallow, and she slows down. Her coach tells her to stop and sit; she refuses, slows to a walk for 30 seconds, presses her hand under the rib, and resumes. Her heart rate at 800 m is 186 beats per minute, and her stroke volume is estimated at 110 mL per beat. Before the race she had hyperventilated for about a minute because she was nervous. After the race she asks why the pain appeared, why walking helped, and whether her pre-race breathing pattern gave her extra oxygen.
1. Calculate her cardiac output at 800 m and compare it with a resting cardiac output of 4.9 L/min. Explain what the difference means for oxygen transport during the race.
Read the worked answer
Cardiac output is heart rate multiplied by stroke volume. At 800 m: 186 beats/min × 110 mL/beat = 20,460 mL/min, or about 20.5 L/min. At rest, 4.9 L/min is given, so exercise cardiac output is about 4.2 times resting. This large rise supports oxygen delivery because cardiac output is the body's central transport pump: more blood per minute means more oxygen can reach the working muscles and more carbon dioxide can be removed. However, at a heart rate of 186, diastolic filling time is short, so stroke volume cannot keep rising and may plateau. Further increases in cardiac output therefore depend mainly on heart rate. That is why a very high heart rate is not automatically better; if filling is compromised, performance can fall even though the heart is beating faster.
2. Explain the likely causes of the side stitch and why slowing to a walk and pressing under the rib helped. Advise a breathing pattern for the rest of the race.
Read the worked answer
A side stitch is usually a mechanical and circulatory problem rather than a sign of heart disease. Possible contributors include strain on the ligaments supporting the diaphragm, reduced blood flow to the diaphragm during intense exercise, a full stomach, and the repeated jarring of running. The sharp pain under the right rib cage fits this pattern. Walking reduces the jarring and lowers the demand on the diaphragm, so the pain eases; pressing with the hand may stabilise the area and reduce stretching. I would advise a regular rhythm rather than shallow chest breathing - for example, inhale for two steps and exhale for two steps, or three-three if that feels comfortable - and avoiding a large meal or sugary drink in the two hours before running. She should not stop completely and sit, because that can make her stiff and drop her heart rate abruptly. If the pain returns with shortness of breath, dizziness, or chest pain, she should stop and be assessed.
3. Evaluate her pre-race hyperventilation. Did it give her extra oxygen? What should she do instead?
Read the worked answer
Hyperventilation did not give her extra oxygen in any useful way. Haemoglobin is already almost fully saturated in healthy adolescents at rest, so extra breathing cannot significantly raise oxygen carrying capacity. What it does do is blow off too much carbon dioxide, causing respiratory alkalosis and narrowing of cerebral blood vessels. That can produce dizziness, light-headedness, tingling, and a false sense that breathing is easier. It may also encourage breath-holding and a sudden urge to gasp at the start. A better routine is slow, controlled breathing - for example, four seconds in and six seconds out for a few minutes - combined with a short warm-up and a simple cue such as 'relax shoulders, steady rhythm'. This lowers unnecessary arousal without disturbing carbon dioxide balance.