Muscle Oxygen Dynamics During Cycling Exercise in Angina Pectoris Patients

Relationship among muscle strength, muscle endurance, and skeletal muscle oxygenation dynamics during ramp incremental cycle exercise

Peak oxygen uptake (VO2), evaluated as exercise tolerance, is a strong predictor of life prognosis regardless of health condition. Several previous studies have reported that peak VO2 is higher in those with a greater decrease in muscle oxygen saturation (SmO2) in the active muscles during incremental exercise. However, the skeletal muscle characteristics of individuals exhibiting a greater decrease in SmO2 during active muscle engagement in incremental exercise remain unclear. This study aimed to clarify the relationship among muscle strength, muscle endurance, and skeletal muscle oxygenation dynamics in active leg muscles during incremental exercise. Twenty-four healthy young men were included and categorized into the non-moderate-to-high muscular strength and endurance group (those with low leg muscle strength, endurance, or both; n = 11) and the moderate-to-high muscular strength and endurance group (those with both moderate-to-high leg muscle strength and endurance; n = 13). All participants underwent cardiopulmonary exercise testing combined with near-infrared spectroscopy to assess whole-body peak VO2 and the change in SmO2 at the lateral vastus lateralis from rest to each exercise stage as skeletal muscle oxygenation dynamics. A linear mixed-effects model, with the change in SmO2 from rest to each stage as the dependent variable, individual participants as random effects, and group and exercise load as fixed effects, revealed significant main effects for both group (P = 0.001) and exercise load (P < 0.001) as well as a significant interaction between the two factors (P < 0.001). Furthermore, multiple-comparison test results showed that the change in SmO2 from rest to 40%-100% peak VO2 was significantly higher in the moderate-to-high muscular strength and endurance group than in the non-moderate-to-high muscular strength and endurance group. Maintaining both muscle strength and endurance at moderate or higher levels contributes to high skeletal muscle oxygenation dynamics (i.e., greater decrease in SmO2) during moderate- or high-intensity exercise.

Interrater reliability of a customized submaximal cycle ergometer test

PURPOSE

Graded exercise testing (GXTs) is used to determine maximum oxygen uptake ([Formula: see text]). Recently, customized submaximal exercise testing (CSET) completed on both treadmill and cycle ergometry were validated.

METHODS

Interrater reliability of the CSET for cycle ergometry was examined. Thirteen participants (age 31 ± 10.2 y, weight 77.9 ± 10.5 kg, height 176.2 ± 9.9 cm, body mass index 25.1 ± 2.9) completed the 2-stage × 3-min CSET protocol performed by two separate testers. True [Formula: see text] was determined using the highest value derived by a GXT and verification bout. Skeletal muscle oxygen saturation ([Formula: see text]), measured using near-infrared spectrometry on the medial gastrocnemius muscle, and [Formula: see text] were monitored during each CSET; whereby, [Formula: see text] kinetics were modeled breath-by-breath data for each 3-min stage. Measurement agreement was quantified using intraclass coefficient (ICC), typical error (TE), and coefficient of variation (CV).

RESULTS

"True" [Formula: see text] (ml·kg^-1·min^-1) between the GXT (41.3 ± 10.5) and verification (42.5 ± 11.5) was established (ICC = 0.98, TE: 0.98, CV 2.1%). Estimated [Formula: see text] by tester 1 (42.5 ± 9.8) and tester 2 (42.7 ± 8.9) did not differ from "true" [Formula: see text] (F_2,36 = 0.02, p = 0.98, η_p² = 0.00). The second stage evoked a [Formula: see text] slow component of 194 ± 124 ml·min^-1 that corresponded with a time-dependent decline of [Formula: see text]. The mean [Formula: see text] from the two CSET testers were highly correlated (ICC = 0.91, TE: 4.1%, CV = 8.9%).

CONCLUSIONS

The CSET is a reliable and valid procedure and [Formula: see text] is a useful tool for corroborating the second stage is in the heavy-intensity domain.