95 Time of single load
The time of single load describes how quickly the body recovers to its resting state after a bout of physical activity with a certain energy expenditure. Recovery requires repaying the oxygen debt, replenishing phosphocreatine and glycogen, clearing lactate and restoring the autonomic balance. It depends on the efficiency of energy production (including oxidation of fatty acids), on haemoglobin's ability to carry and release oxygen, and on thyroid hormones. A clinically established measure of recovery is the heart rate recovery: how much the heart rate falls in the first minute after exercise, which reflects the return of parasympathetic (vagal) tone.
Clinical significance
In a study of patients referred for exercise testing, a heart rate fall of 12 beats/min or less in the first minute after stopping was associated with twice the risk of death after adjustment for other factors, independently of exercise capacity and myocardial perfusion. Slow recovery after load is also seen with deconditioning, heart failure, autonomic neuropathy (for example in diabetes), anaemia, hypothyroidism, chronic lung disease, overtraining and after illness.
Unusual breathlessness, chest discomfort, dizziness or very slow recovery after ordinary activity need medical assessment, possibly with an exercise test.
References
- Cole CR, Blackstone EH, Pashkow FJ, Snader CE, Lauer MS. Heart-rate recovery immediately after exercise as a predictor of mortality. N Engl J Med. 1999;341(18):1351–1357. doi:10.1056/NEJM199910283411804
- American Thoracic Society; American College of Chest Physicians. ATS/ACCP statement on cardiopulmonary exercise testing. Am J Respir Crit Care Med. 2003;167(2):211–277. doi:10.1164/rccm.167.2.211
This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.
Published on 5 May 2024