Effects of CHO-electrolyte solution intake on heart rate at a given VO2 during mountaineering in middle-aged and older subjects

 

Ken Miyagawa^1,2, Keiko Matsukawa¹, Yoshi-ichiro Kamijo¹, Yoshiyuki Maruoka², and Hiroshi Nose^1,2

¹Department of Sports Medical Sciences, Shinshu University Graduate School of Medicine; ²Jukunen Taiiku Daigaku Research Center, Matsumoto 390-8621, Japan

 

We have developed a tri-axial accelerometer to estimate oxygen consumption rate (VO₂) during uphill and downhill walking. Using this, we examined whether heart rate (HR) at a given VO₂ was attenuated by carbohydrate-electrolyte solution (CE) than by tap water (TW) during mountain climbing in middle-aged older subjects.  Eighteen subjects (~63 yr) were divided into the TW and CE groups. In September, 2008, they climbed from 1260m to 2360m while HR and VO₂ were monitored. Total time, VO₂, sweat loss, and fluid intake to reach the destination were 270min, 850kcal, 1.5 litter, and 0.9 litters, respectively, with no significant differences between groups. HR was significantly correlated with VO₂ during climbing in all subjects (P<0.05). Although the slope of changes in HR and VO₂ (ΔHR/ΔVO₂) for the first 60 min of climbing was similar to that for the last 60 min in both groups, the intercept increased by 12 beats•min^-1 in TW while it remained unchanged in CE with significance between groups (P<0.05). Thus, CE attenuated HR at a given VO₂ more than TW in middle-aged and older subjects.

 

Key words: mountain climbing, fluid intake, fatigue