Luke A. Willis, Andrew T. Singer, Brian Parr, FACSM. University of South Carolina Aiken, Aiken, SC.

BACKGROUND: Regular exercise can improve fitness and physical, mental, and emotional wellbeing. Research shows the influence of exercise environment on exercise benefits, implying that indoor and outdoor exercise have different effects on physical, mental, and emotional responses. This may be because even though people tend to exercise at a higher intensity outside, it may feel easier. Most of these studies compare indoor and outdoor exercise done in a comfortable environment. The responses to exercise may be different in more extreme temperatures. The purpose of this study was to compare the physiological (heart rate, body temp, blood lactate) and psychological (RPE) responses to indoor and outdoor exercise in a hot environment. METHODS: Subjects completed three 30-minute exercise sessions on a cycle ergometer set at the same intensity in three conditions: Indoor cool (I) in the fitness center, outdoor hot (O) on a covered porch, and indoor hot (S) in a temperature-controlled sauna. The HR, body temp, and RPE were recorded at rest and throughout exercise and blood lactate was measured at the end of exercise. RESULTS:  The air temperature (O: 33.7±2.7 °C and S: 35.7±3.1 °C vs. I: 22.4±0.5 °C, p<0.001) and heat index (O: 38.5±4.2 and S: 45.0±8.1 vs. I: 22.3±0.5, p<0.001) were significantly higher in the two hot conditions (O, S) compared to indoors (I). The exercise intensity was matched between conditions (I: 82.9±33.5 W, O: 82.9±32.8 W, S: 83.3±33.5 W, p=0.98). The HR (O: 157.8±13.7 and S: 161.4±12.0 vs. I: 143.5±13.6, p<0.05), % max HR (O: 82.6±5.9% and S: 84.5±4.7% vs. I: 75.1±6.1%, p<0.01), body temperature (O: 36.8±0.4 °C and S: 37.5±0.4 °C vs. I: 36.2±0.2 °C, p<0.001), and RPE (O: 14.0±2.0 and S: 14.5±2.3 vs. I: 12.7±1.5, p<0.05) were significantly higher in the O and S conditions compared to indoors. The differences in postexercise blood lactate were not statistically significant (I: 5.1±1.8 mmol/L, O: 6.3±2.2 mmol/L, S: 4.3±1.2 mmol/L, p=0.98). CONCLUSION: This study shows that exercise at the same work rate leads to greater physiological and psychological responses consistent with higher intensity work in a hot environment, both indoors and outdoors. This suggests that some of the benefits of outdoor exercise may not apply to hot, humid conditions.

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