title: Variability of cardio-respiratory, electromyographic, and perceived exertion responses at the walk-run transition in a sample of young men controlled for anthropometric and fitness characteristics.
abstract: The cardio-respiratory (heart rate, HR; oxygen uptake, VO(2;) expired carbon dioxide, VCO(2); ventilation, VE), electromyographic (EMG; medial gastrocnemius, vastus lateralis, rectus femoralis, and anterior tibialis), and perceived exertion (PE) responses during a protocol for the determination of the walk-run transition speed (WRTS) were investigated. From an initial sample of 453 volunteers, 12 subjects matched for age, anthropometric characteristics [height, weight, lower limb length (LLL)], cardio-respiratory fitness (peak oxygen consumption, VO(2peak); ventilatory threshold, VT; maximal HR), and habitual physical activity levels were selected (age = 18.6 ± 0.5 years; height = 174.5 ± 1.4 cm; weight = 66.4 ± 1.1 kg; LLL = 83.3 ± 1.2 cm, VO(2peak) = 52.2 ± 2.2 ml kg(-1) min(-1); VT = 39.8 ± 2.6 ml kg(-1) min(-1)). The highly reproducible WRTS determination protocol (ICC = 0.92; p < 0.0001) consisted in 2-min warm-up at 5.5 km h(-1) followed by increments of 0.1 km h(-1) every 15 s. Between-subjects variability of the measured variables during 24 walking and 12 running velocities (from 80 to 120% of WRTS) was compared to WRTS variation. The coefficient of variation for WRTS was 7.8%, which was within the range of variability for age, anthropometric variables, VO(2peak), and maximal HR (from 5 to 12%). Cardio-respiratory responses at WRTS had a greater variation (VO(2) about 50%; VE/VCO(2) about 35%; VE/VO(2) about 45%; HR about 30%). The highest variation was found for PE (from 70 to 90%) whereas EMG variables showed the lowest variation (from 25 to 30%). Linear regression between EMG series and VO(2) data showed that VO(2) reflected the increase in muscle activity only before the WRTS. These results support the hypothesis that the walk-run transition phenomenon is determined by mechanical variables such as limb length and its relationship to biomechanical model rather than by metabolic factors.
authors.affiliation: Universidade do Estado do Rio de Janeiro (UERJ), Rio de Janeiro, RJ, Brazil.
authors.forename: Walace D
authors.initials: WD
authors.lastname: Monteiro
authors.forename: Paulo T V
authors.initials: PT
authors.lastname: Farinatti
authors.forename: Carlos G
authors.initials: CG
authors.lastname: de Oliveira
authors.forename: Claudio Gil S
authors.initials: CG
authors.lastname: Araújo
mesh_terms: D000293:Adolescent; D000886:Anthropometry; D001837:Body Weights and Measures; D016022:Case-Control Studies; D015331:Cohort Studies; D004576:Electromyography; D005080:Exercise Test / Q000379:methods; D006321:Heart / Q000502:physiology*; D006801:Humans; D007206:Individuality; D008297:Male; D010465:Perception / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D012119:Respiration; D012420:Running / Q000502:physiology*; D016138:Walking / Q000502:physiology*; D055815:Young Adult