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Christopher Byrne and Jason K.W. Lee

Purpose: To determine if the Physiological Strain Index (PSI), in original or modified form, can evaluate heat strain on a 0–10 scale, in trained and heat-acclimatized men undertaking a competitive half-marathon run in outdoor heat. Methods: Core (intestinal) temperature (TC) and heart rate (HR) were recorded continuously in 24 men (mean [SD] age = 26 [3] y, VO2peak = 59 [5] mL·kg·min−1). A total of 4 versions of the PSI were computed: original PSI with upper constraints of TC 39.5°C and HR 180 beats·min−1 (PSI39.5/180) and 3 modified versions of PSI with each having an age-predicted maximal HR constraint and graded TC constraints of 40.0°C (PSI40.0/PHRmax), 40.5°C (PSI40.5/PHRmax), and 41.0°C (PSI41.0/PHRmax). Results: In a warm (26.1–27.3°C) and humid (79–82%) environment, all runners finished the race asymptomatic in 107 (10) (91–137) min. Peak TC and HR were 39.7°C (0.5°C) (38.5–40.7°C) and 186 (6) (175–196) beats·min−1, respectively. In total, 63% exceeded TC 39.5°C, 71% exceeded HR 180 beats·min−1, and 50% exceeded both of the original PSI upper TC and HR constraints. The computed heat strain was significantly greater with PSI39.5/180 than all other methods (P < .003). PSI >10 was observed in 63% of runners with PSI39.5/180, 25% for PSI40.0/PHRmax, 8% for PSI40.5/PHRmax, and 0% for PSI41.0/PHRmax. Conclusions: The PSI was able to quantify heat strain on a 0–10 scale in trained and heat-acclimatized men undertaking a half-marathon race in outdoor heat, but only when the upper TC and HR constraints were modified to 41.0°C and age-predicted maximal HR, respectively.

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Genevieve Fridlund Dunton, Donna Spruijt-Metz, Jennifer Wolch, Chih-Ping Chou, Michael Jerrett, Jason Byrne, Susan Weaver and Kim D. Reynolds


Efforts to increase community levels of physical activity through the development of multiuse urban trails could be strengthened by information about factors predicting trail use. This study examined whether reasons for trail use predict levels of physical activity on urban trails.


Adults (N = 335) living within a 1-mile buffer zone of urban trails in Chicago, Dallas, and Los Angeles completed a self-report measure assessing demographics, reason for trail use, and physical activity on the trail. Accelerometers measured total daily moderate-to-vigorous physical activity (MVPA). Environmental features of the urban trail were assessed with the Systematic Pedestrian and Cyclist Environmental Scan for trails measure. Multivariate regression analyses were conducted that accounted for clustering of individuals within trail segments.


After controlling for demographic and environmental factors and total daily MVPA, reasons for trail use significantly predicted recreational but not transportation activity. Recreational trail activity was greater for participants who reported exercise and health reasons for trail use as compared with other reasons (ie, social interaction, enjoying nature, walking pets) for recreational trail use.


To increase the use of urban trails, it may be useful to promote the health and exercise benefits of recreational trail use.

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Christopher Johansen, Kim D. Reynolds, Jennifer Wolch, Jason Byrne, Chih-Ping Chou, Sarah Boyle, Donna Spruijt-Metz, Brianna A. Lienemann, Susan Weaver and Michael Jerrett

Background: Urban trails are a useful resource to promote physical activity. This study identified features of urban trails that correlated with trail use. Methods: Multiuse urban trails were selected in Chicago, Dallas, and Los Angeles. An audit of each trail was completed using the Systematic Pedestrian and Cyclist Environmental Scan for Trails instrument, identifying built environmental features. A self-report of trail use was obtained from trailside residents (N = 331) living within 1 mile of each trail. Univariate and multivariate Poisson regressions controlled for trail time from home and motivation for physical activity. Results: Positive associations with the past month’s hours on the trail were observed for the presence of distance signs, vegetation height, vegetation maintenance, and trail crowding, and a negative association was observed for the presence of crossings on the trail. Positive associations with dichotomous trail use were observed for the presence of distance signs, vegetation height, and vegetation maintenance, and a negative association was observed for the presence of crossings on the trail. Conclusions: These correlates should be confirmed in other studies and, if supported, should be considered in the promotion and design of urban trails.