Forty-three men (age 33 +/- 9 yr) with spinal cord injuries (SCI) were observed during a normal workday while heart rate was recorded continuously. Physical strain was estimated using the heart rate response expressed relative to the individual heart rate reserve (%HRR). The mean physical strain during the day for group I (C4-C8, N = 9), II (T1-T5, N = 6), III (T6-T10, N = 15), and IV (T10-L5, N = 13) was 38 +/- 8, 29 +/- 12, 22 +/- 8, and 23 +/- 5%HRR, respectively. Prolonged periods (> 15 min) of high strain (> 60%HRR) that might maintain or improve physical capacity were not identified during activities of daily life (ADL), but only during sports activities. The analysis of activity-related strain revealed that specific ADL such as making transfers, entering/leaving car, and negotiating environmental barriers, provoked high levels of strain, especially in those with quadriplegia. Periods of peak strain (> 60%HRR, < 3 min) occurred frequently, also predominantly in those with quadriplegia. It was concluded that the physical strain during ADL is related to the level of lesion and is not of a magnitude and duration that would maintain or improve physical capacity. The periods of peak strain might restrict the mobility and independence of persons with SCI, and, therefore, reduce their quality of life.