Comparison of Resistance-Based Walking Cardiorespiratory Test to the Bruce Protocol

Abstract

Hurt, CP, Bamman, M, Naidu, A, and Brown, DA. Comparison of resistance-based walking cardiorespiratory test to the Bruce Protocol. J Strength Cond Res 34(12): 3569-3576, 2020-Cardiorespiratory fitness is assessed through graded exercise tests that determine the maximum amount of sustained mechanical work that an individual can perform while also providing health- and fitness-related information. This article describes a novel method to perform graded exercise tests that use posteriorly directed resistive forces. The purpose of this investigation was to validate a novel resistance-based test (RBT) in comparison with a traditional speed- and incline-based test (SIBT) in a cohort of nonimpaired individuals. Twenty nonimpaired individuals, 8 men and 20 women age 28.4 ± 9.6, range 20-54 years old performed 2 maximal exercise tests. The SIBT used the Bruce Protocol and increased treadmill incline and speed every 3 minutes. The RBT used a robotic device interfaced with the treadmill that provided specified horizontal resistive forces at the center of mass calculated to match each Bruce Protocol stage while individuals walked at 1.1 m·s. Subjects obtained ∼3% higher maximum V[Combining Dot Above]O2 measure using the speed- and incline-based method (dependent t-test p = 0.08). V[Combining Dot Above]O2peaks between tests were strongly correlated (r = 0.93, p < 0.001). Peak values of secondary physiologic measures (i.e., max heart rate and respiratory exchange ratio) were within 3% between tests. We found a significant linear relationship between mass-specific work rate and measured V[Combining Dot Above]O2 stage by stage for both tests, but no significant difference between each linear fit (p = 0.84). These data suggest that horizontal resistive forces, while walking on a treadmill, can be used to increase aerobic effort in a way that closely simulates work rates of the Bruce Protocol.

Figure 1

Example of the experimental setup for the resistance-based tests that used a rehabilitation robot. Individuals were asked to maintain an average walking speed of 1.1 m/s throughout the duration of the test. The device allows for fluctuations in walking speed, similar to that seen during normal overground walking; thus, individuals were provided a targeted range within which they maintained the speed trace of the treadmill belt (A). The resistive force that the participant must overcome is also depicted on this screen (e.g., 53 lbs pictured in the upper left corner of A.). The participant controlled speed of the treadmill belt based on measured forces (i.e., via bilateral force transducers) embedded in the pelvic mechanisms (B) and a linear, force-velocity relationship.

Figure 2

The relationship between repeated peak exercise tests using a speed and incline based test (SIBT) and a resistance based test (RBT). We observed a strong linear relationship between tests. The tests did not align perfectly with the line of identity (dark black line).

Figure 3

Differences in peak V̇O₂ between tests as a percentage. We observed that 7 individuals nominally achieve a higher V̇O_2peak using the resistance based test. The average difference between test, pictured at the end of the bar chart was ~2.5%.