By the addition of externally added elastic loads at both functional residual capacity (FRC) and increased lung volume, increased respiratory muscle effort, tension, and breathlessness were induced in normal subjects. The magnitude of each of these sensations was estimated using the psychophysical technique of category scaling (Med. Sci. Sports Exercise 14: 377-381, 1982). The tidal volume, inspiratory time, and breathing frequency were kept constant to avoid variability in sensation due to these factors. The perceived magnitude of effort and breathlessness increased significantly as the inspiratory pressure and lung volume increased (P less than 0.05). The magnitude of perceived tension increased as the inspiratory pressure increased (P less than 0.05) but not as lung volume increased. To validate these results, the subjects estimated the perceived magnitude of a series of static inspiratory occlusion pressures at both lung volumes using open-magnitude scaling and sensory matching. The perceived magnitude of effort increased significantly as the pressure increased and as the lung volume increased (P less than 0.05). To match the perceived effort required to produce the target pressures at FRC, the subjects reproduced pressures. These were not significantly different. However, to match the effort required to produce the target pressures at increased lung volume, the pressures reproduced at FRC were significantly greater (P less than 0.05). The results suggest that the sensations of breathlessness and effort are psychophysically the same, whereas tension is perceived by a different sensory mechanism.

The present study re-evaluated the accuracy of standards for maximal exercise capacity (Wcap) recently reported from our laboratory by examining the interaction between height and age on Wcap achieved and predicted in 1,071 subjects (732 males and 339 females). They underwent an incremental exercise test on a cycle ergometer using the same incremental protocol and exercise mode as the previous study, and were retrospectively judged to be normal. Although Wcap predicted was either not significantly different (males) or underestimated Wcap by less than 5% (females, p less than 0.05), significant differences were found in subjects at the extremes of the population ranges for height and age. The influences of age 9yr) and height (m) were found to be nonlinear and interactive, as described by the equations: Males: Wcap = 1506*Ht2.70*Age-0.46(r = 0.78) (lower limit 81% pred) Females: Wcap = 969*Ht2.80*Age-0.43(r = 0.77) (lower limit 79% pred) Wcap (kpm/min) predicted by these equations was compared to Wcap achieved by the 100 subjects who took part in the original study; no significant differences were found (paired t test, p less than 0.05). The interactive influences of age and height expressed by the equations are more plausible from a biological point of view than the linear, additive relationships previously described. The equations should be more reliable than previous equations for patients referred for exercise testing.

The capacity of inspiratory muscles to generate esophageal pressure at several lung volumes from functional residual capacity (FRC) to total lung capacity (TLC) and several flow rates from zero to maximal flow was measured in five normal subjects. Static capacity was 126 +/- 14.6 cmH2O at FRC, remained unchanged between 30 and 55% TLC, and decreased to 40 +/- 6.8 cmH2O at TLC. Dynamic capacity declined by a further 5.0 +/- 0.35% from the static pressure at any given lung volume for every liter per second increase in inspiratory flow. The subjects underwent progressive incremental exercise to maximum power and achieved 1,800 +/- 45 kpm/min and maximum O2 uptake of 3,518 +/- 222 ml/min. During exercise peak esophageal pressure increased from 9.4 +/- 1.81 to 38.2 +/- 5.70 cmH2O and end-inspiratory esophageal pressure increased from 7.8 +/- 0.52 to 22.5 +/- 2.03 cmH2O from rest to maximum exercise. Because the estimated capacity available to meet these demands is critically dependent on end-inspiratory lung volume, the changes in lung volume during exercise were measured in three of the subjects using He dilution. End-expiratory volume was 52.3 +/- 2.42% TLC at rest and 38.5 +/- 0.79% TLC at maximum exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

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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 (Wcap) 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% Wcap, muscle tension was just noticeable at 31 +/- 16% Wcap, muscle discomfort was just noticeable at 47 +/- 21% Wcap, breathing discomfort was just noticeable at 52 +/- 19% Wcap, and muscle pain was just noticeable at 58 +/- 33% Wcap. The intensity of all sensations increased in a positively accelerating manner with increases in power output (P < 0.001). Above 60% Wcap, the intensity of leg effort and muscle tension exceeded the intensity of muscle pain (P < 0.01), and above 100% Wcap the intensity of muscle discomfort also exceeded the intensity of muscle pain (P < 0.01). At 120% Wcap, 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.