Quantification of intensity of sensations during muscular work by normal subjects

Eleven subjects performed a series of 30-s work bouts on a cycle ergometer at power outputs ranging from 20-120% of the work capacity (W-cap) achieved during an incremental cycle to exhaustion and estimated the intensity of several sensations (leg effort, muscle tension, muscle discomfort, muscle pain, and breathing discomfort) by using Borg's category-ratio scale (range 0-10 units). Leg effort was perceived as ''just noticeable'' at 31 +/- 15% W-cap, muscle tension was just noticeable at 31 +/- 16% W-cap muscle discomfort was just noticeable at 47 +/- 21% W-cap, breathing discomfort Tvas just. noticeable at 52 +/- 19% W-cap and muscle pain mas just noticeable at 58 +/- 33% W-cap. The intensity of all sensations increased in a positively accelerating manner with increases in power output (P < 0.001). Above 60% W-cap, the intensity of leg effort and muscle tension exceeded the intensity of muscle pain (P < 0.01), and above 100% W-cap the intensity of muscle discomfort also exceeded the intensity of muscle pain (P < 0.01). At 120% W-cap, leg effort, muscle tension; and muscle discomfort were rated between ''severe'' and ''very severe'' (6.1 +/- 2.2, 6.4 +/- 2.0, and 5.6 +/- 2.1 Borg units, respectively), whereas muscle pain and breathing discomfort were rated between ''moderate'' and ''somewhat severe'' (3.6 +/- 2.1 and 3.3 +/- 1.9 Borg units, respectively). These results suggest that subjects have a perception of muscle pain during muscular work that is distinct from perceptions of leg effort, muscle tension, and muscle discomfort.