Short-term effects of exercise

Short-term effects happen during and straight after exercise, then wear off.

• Muscle temperature rises, because working muscles release heat. Warm muscles are more pliable and contract faster.
• Heart rate rises, so blood is pumped round faster.
• Stroke volume rises, so more blood leaves the heart with each beat.
• So cardiac output rises: more blood, carrying more oxygen, reaches the working muscles each minute.

Heart rate often rises a little just before exercise, as the body gets ready: this is the anticipatory rise.

The graph shows one person's heart rate before, during and after 15 minutes of steady running. The data was written for this app.

• A: the anticipatory rise, just before exercise starts.
• B: during steady exercise, heart rate rises quickly, then levels off once the heart is supplying enough oxygen.
• C: after exercise, heart rate falls quickly, then more slowly, back towards resting. This is recovery.

• Redistribution of blood flow: during exercise, more blood is sent to the working muscles and less to organs that aren't needed as much, such as the stomach and intestines. That's why it's best not to eat a big meal just before sport.
• Respiratory rate (breathing rate), tidal volume and so minute ventilation all rise, so more air is breathed in and out each minute.
• Together these deliver more oxygen to the working muscles, and remove more carbon dioxide.

Example: in the second half of a hockey match, a midfielder's legs receive far more of the blood flow than at rest.

During high-intensity exercise, the muscles can't get enough oxygen, so they work anaerobically and produce lactic acid. Lactic acid builds up and causes fatigue: the muscles feel heavy and painful, and the performer has to slow down. A 400 m runner often slows in the last 100 m for this reason. Breathing stays fast after exercise, to supply the extra oxygen needed to remove it.

Collecting data: heart rate can be measured by counting the pulse at the wrist or neck for 15 seconds and multiplying by 4, or with a heart-rate monitor. Breathing rate can be counted the same way.