Lower rate-pressure product during submaximal walking: a link to fatigue improvement following a physical activity intervention among breast cancer survivors

Abstract

Purpose: Research showing a link between exercise-induced changes in aerobic fitness and reduced fatigue after a cancer diagnosis has been inconsistent. We evaluated associations of fatigue and rate-pressure product (RPP), a reliable index of myocardial oxygen demand, at rest and during submaximal walking following a physical activity intervention among post-primary treatment breast cancer survivors (BCS).

Methods: Secondary analyses of 152 BCS in a randomized controlled trial testing a physical activity intervention (INT) versus usual care (UC) were performed. The INT group completed counseling/group discussions along with supervised exercise sessions tapered to unsupervised exercise. Evaluations were made at baseline and immediately post-intervention (M3) on measures of physical activity (accelerometry), graded walk test, and average fatigue over the previous 7 days. RPP was calculated by dividing the product of heart rate and systolic blood pressure by 100.

Results: Resting and submaximal RPPs were significantly improved in both groups at M3; however, the magnitude of change (∆) was greater in the INT group from stage 1 (∆RPP1; INT -13 ± 17 vs. UC -7 ± 18; p = 0.03) through stage 4 (∆RPP4; INT -21 ± 26 vs. UC -9 ± 24; p < 0.01) of the walk test. The INT group reported significantly reduced fatigue (INT -0.7 ± 2.0 vs. UC +0.1 ± 2.0; p = 0.02) which was positively associated with ∆RPP during stages 2-4 of the walk test but not ∆aerobic fitness.

Conclusions: Lower RPP during submaximal walking was significantly associated with reduced fatigue in BCS.

Implications for cancer survivors: Exercise/physical activity training programs that lower the physiological strain during submaximal walking may produce the largest improvements in reported fatigue.

Keywords: Cardiovascular; Exercise; Heart rate; Systolic blood pressure.

Figure 1

Data expressed as means ± s.e.m. Changes (Δ) in rate-pressure product among intervention and usual care groups from baseline to month 3 (M3) follow-up. **Significantly lower (p < 0.05) rate-pressure product in intervention group emerging at Stage 1 through Stage 4 of the modified Naughton protocol. P-value indicates a significant linear time by group interaction.