Impact of Direction of Unloading Influence on Template Rate of Perceived Exertion.

Greer, BK, Young, PR, Thompson, B, Rickert, BJ, and Moran, MF. Impact of direction of unloading influence on template rate of perceived exertion. J Strength Cond Res 32(12): 3407-3413, 2018-It is suggested that exercisers engage in a process of teleoanticipation and create an exercise template based on previous experience with the exercise task that guides their perceptions of the amount of effort required for task completion. This study examined how altering workload intensity during a positive-pressure treadmill task may impact Rating of Perceived Exertion (RPE). In a counterbalanced design, 15 collegiate cross-country runners (7 men and 8 women) performed 2 25-minute runs at a constant velocity, while body mass (BM) was either increased from 60 to 100% (low-to-high progression trial [INC]) or decreased from 100 to 60% (high-to-low progression trial) in 5-minutes increments. Oxygen consumption (V[Combining Dot Above]O2), heart rate (HR), and respiratory exchange ratio (RER) were collected. RPE was recorded at the end of each stage, and energy expenditure (EE) was calculated with V[Combining Dot Above]O2 and RER data. There were no significant differences between direction of loading conditions for V[Combining Dot Above]O2, EE, HR, and RER (p > 0.05). Between-trial differences in RPE at 100, 90, and 80% BM were statistically significant (p < 0.001), with higher RPEs observed during the INC. Differences in RPE observed between conditions cannot be explained by physiological mechanisms. These findings suggest that RPE is a multifaceted construct that can be impacted by subjectively based anticipatory factors such as exercise intensity.

Tibial Acceleration and Spatiotemporal Mechanics in Distance Runners During Reduced-Body-Weight Conditions.

CONTEXT: Treadmills that unload runners via a differential air-pressure (DAP) bladder (eg, AlterG Anti-Gravity Treadmill) are commonly used to reduce effective body weight (BW) in a clinical setting. However, the relationship between the level of unloading and tibial stress is currently unknown. OBJECTIVE: To determine the relationship between tibial impact acceleration and level of BW unloading during running. DESIGN: Cross-sectional. SETTING: University motion-analysis laboratory. PARTICIPANTS: 15 distance runners (9 male, 6 female; 20.4 ± 2.4 y, 60.1 ± 12.6 kg). MAIN OUTCOME MEASURES: Peak tibial acceleration and peak-to-peak tibial acceleration were measured via a uniaxial accelerometer attached to the tibia during a 37-min continuous treadmill run that simulated reduced-BW conditions via a DAP bladder. The trial began with a 10-min run at 100% BW followed by nine 3-min stages where BW was systematically reduced from 95% to 60% in 5% increments. RESULTS: There was no significant relationship between level of BW and either peak tibial acceleration or peak-to-peak tibial acceleration (P > .05). Both heart rate and step rate were significantly reduced with each 5% reduction in BW level (P < .01). CONCLUSIONS: Although ground-reaction forces are reduced when running in reduced-BW conditions on a DAP treadmill, tibial shock magnitudes are unchanged as an alteration in spatiotemporal running mechanics (eg, reduced step rate) and may nullify the unloading effect.