title: Near-Infrared Spectroscopy: More Accurate Than Heart Rate for Monitoring Intensity in Running in Hilly Terrain.
abstract: OBJECTIVE
  To investigate the cardiorespiratory and metabolic response of trail running and evaluate whether heart rate (HR) adequately reflects the exercise intensity or if the tissue-saturation index (TSI) could provide a more accurate measure during running in hilly terrain.
  
  
  METHODS
  Seventeen competitive runners (4 women, V̇O2max, 55 ± 6 mL · kg-1· min-1; 13 men, V̇O2max, 68 ± 6 mL · kg-1· min-1) performed a time trial on an off-road trail course. The course was made up of 2 laps covering a total distance of 7 km and included 6 steep uphill and downhill sections with an elevation gain of 486 m. All runners were equipped with a portable breath-by-breath gas analyzer, HR belt, global positioning system receiver, and near-infrared spectroscopy (NIRS) device to measure the TSI.
  
  
  RESULTS
  During the trail run, the exercise intensity in the uphill and downhill sections was 94% ± 2% and 91% ± 3% of maximal heart rate, respectively, and 84% ± 8% and 68% ± 7% of V̇O2max, respectively. The oxygen uptake (V̇O2) increased in the uphill sections and decreased in the downhill sections (P < .01). Although HR was unaffected by the altering slope conditions, the TSI was inversely correlated to the changes in V̇O2(r = -.70, P < .05).
  
  
  CONCLUSIONS
  HR was unaffected by the continuously changing exercise intensity; however, TSI reflected the alternations in V̇O2. Recently used exclusively for scientific purposes, this NIRS-based variable may offer a more accurate alternative than HR to monitor running intensity in the future, especially for training and competition in hilly terrain.
authors.forename: Dennis-Peter
authors.initials: DP
authors.lastname: Born
authors.forename: Thomas
authors.initials: T
authors.lastname: Stöggl
authors.forename: Mikael
authors.initials: M
authors.lastname: Swarén
authors.forename: Glenn
authors.initials: G
authors.lastname: Björklund
mesh_terms: D000328:Adult; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D010101:Oxygen Consumption; D012420:Running / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared; D055815:Young Adult
keywords: athlete; elite; tissue saturation; undulating terrain