Breathing valve resistance alters physiological responses during a graded exercise test.

PURPOSE: To determine the impact of breathing valve resistance on peak aerobic capacity ([Formula: see text]) and running economy (RE) in endurance-trained and recreationally active individuals. METHODS: Ten endurance-trained males (ETM), 10 endurance-trained females (ETF), 10 recreationally active males (RAM), and 10 recreationally active females (RAF) participated in this study. On two separate occasions, subjects performed identical graded exercise treadmill protocols using either a Hans Rudolph 2700 (high resistance) or a Daniels' (low resistance) two-way non-rebreathing valve. Parameters obtained from these protocols included energy expenditure (EE), ventilation ([Formula: see text]), heart rate, respiratory exchange ratio, RE, [Formula: see text], and time to exhaustion (TTE). RESULTS: When using the Daniels' valve, all groups had lower submaximal EE (- 2.4, - 3.4, - 2.7, and - 2.0% for ETM, ETF, RAM, and RAF) and better RE (- 2.7, - 3.5, - 1.9, and - 1.8% for ETM, ETF, RAM and RAF) across all submaximal speeds. Only the ET groups had lower submaximal [Formula: see text] (4.6 and 3.8% for ETM and ETF) when using the Daniels' valve. TTE increased when using the Daniels' valve for all groups (6.0, 10.9, 6.2 and 9.8% for ETM, ETF, RAM and RAF), but [Formula: see text] was unaltered. CONCLUSION: Compared to the Daniels' valve, the Hans Rudolph 2700 valve altered the assessment of RE, submaximal EE, and TTE regardless of fitness level or sex, but did not change [Formula: see text]. Therefore, airflow resistance of a breathing valve must be considered when assessing and comparing EE, RE and TTE in the applied and research settings.

Beneficial Effects of Cooling during Constant Power Non-steady State Cycling.

This study compared the effects of cooling on the energetic and associated physiological and perceptual responses to constant power, non-steady state cycling. Twelve males cycled at their lactate threshold power for 60 min or until exhaustion under 3 conditions: wearing a cooling vest and sleeves (COOL), a synthetic shirt embedded with an active particle technology claimed to facilitate evaporative heat loss (EVAP), and a standard synthetic shirt (CON). When adjusted for time, the increase in gastrointestinal temperature from baseline was reduced during COOL and EVAP compared to CON (1.44±0.45 and 1.52±0.43 vs. 1.66±0.45°C, p<0.05). Sweat rate was reduced during COOL compared to EVAP and CON (1 312±331 vs. 1 525±393 and 1 550±548 mL·h-1, p<0.01). Gross efficiency decreased over time across conditions (p<0.01), but COOL attenuated this decrease by 22% compared to CON (p<0.05). The rating of perceived exertion was reduced during COOL and EVAP compared to CON (p<0.01). In conclusion, cooling using a vest and sleeves or wearing an active particle technology shirt reduced the rise in gastrointestinal temperature and rating of perceived exertion compared to a standard synthetic shirt. Cooling using a vest and sleeves also reduced the decrease in gross efficiency and sweat rate compared to wearing the standard synthetic shirt.

Measuring changes in aerodynamic/rolling resistances by cycle-mounted power meters.

PURPOSE: To develop a protocol for isolating changes in aerodynamic and rolling resistances from field-based measures of power and velocity during level bicycling. METHODS: We assessed the effect of body position (hands on brake hoods vs drops) and tire pressure changes (414 vs 828 kPa) on aerodynamic and rolling resistances by measuring the power (Pext)-versus-speed (V) relationship using commercially available bicycle-mounted power meters. Measurements were obtained using standard road bicycles in calm wind (<1.0 m·s) conditions at constant velocities (acceleration <0.5 m·s) on a flat 200-m section of a smooth asphalt road. For each experimental condition, experienced road cyclists rode in 50-W increments from 100 to 300 W for women (n=2) or 100 to 400 W for men (n=6). Aerodynamic resistance per velocity squared (k) was calculated as the slope of a linear plot of tractive resistance (RT=power/velocity) versus velocity squared. Rolling resistance (Rr) was calculated as the intercept of this relationship. RESULTS: Aerodynamic resistance per velocity squared (k) was significantly greater (P<0.05) while riding on the brake hoods compared with the drops (mean ± SD: 0.175 ± 0.025 vs 0.155 ± 0.03 N·V). Rolling resistance was significantly greater at 60 psi compared with 120 psi (5.575 ± 0.695 vs 4.215 ± 0.815 N). CONCLUSIONS: These results demonstrate that commercially available power meters are sensitive enough to independently detect the changes in aerodynamic and rolling resistances associated with modest changes in body position and substantial changes in tire pressure.