OBJECTIVE: The aim of this study was to investigate safety, tolerance, relative exercise intensity, and muscle substrate oxidation during sessions performed on a Huber Motion Lab in coronary heart disease patients. DESIGN: After an assessment of Vo2 peak, 20 coronary heart disease patients participated in two different exercises performed in random order at 40% and 70% (W40 and W70) of the maximal isometric voluntary contraction. RESULTS: No significant arrhythmia or abnormal blood pressure responses occurred during either session, and no muscle soreness was reported within 48 hrs posttest. The authors found a difference between W40 and W70 sessions for mean (standard deviation) ventilation (25.1% [8%] and 32.1% [9%] of maximal ventilation, respectively; P = 0.04) and a small difference for mean (standard deviation) heart rate (73 [7] and 79 [8] beats/min, respectively; P < 0.01). When compared with the W40, the W70 was associated with higher active energy expenditure (2.4 [0.6] and 3.1 [0.9] Kcal/min, respectively; P < 0.0001) and a similar mean (standard deviation) oxygen uptake (5.5 [1] and 6.6 [1] ml/min per kilogram, respectively; P = 0.07). The qualitative percentages of carbohydrates and lipids oxidized were 71% and 29%, respectively, at W40 and 91% and 9%, respectively, at W70. CONCLUSIONS: Both protocols, which consisted of repeating 6-sec phases of contractions with 10 secs of passive recovery on the Huber Motion Lab, seemed to be well tolerated, safe, and feasible in this group of coronary heart disease patients.