Accelerated Muscle Deoxygenation in Aerobically Fit Subjects During Exhaustive Exercise Is Associated With the ACE Insertion Allele

Abstract

Introduction: The insertion/deletion (I/D) polymorphism in the gene for the major regulator of vascular tone, angiotensin-converting enzyme-insertion/deletion (ACE-I/D) affects muscle capillarization and mitochondrial biogenesis with endurance training. We tested whether changes of leg muscle oxygen saturation (SmO₂) during exhaustive exercise and recovery would depend on the aerobic fitness status and the ACE I/D polymorphism.

Methods: In total, 34 healthy subjects (age: 31.8 ± 10.2 years, 17 male, 17 female) performed an incremental exercise test to exhaustion. SmO₂ in musculus vastus lateralis (VAS) and musculus gastrocnemius (GAS) was recorded with near-IR spectroscopy. Effects of the aerobic fitness status (based on a VO_2peak cutoff value of 50 ml O₂ min^-1 kg^-1) and the ACE-I/D genotype (detected by PCR) on kinetic parameters of muscle deoxygenation and reoxygenation were assessed with univariate ANOVA.

Results: Deoxygenation with exercise was comparable in VAS and GAS (p = 0.321). In both leg muscles, deoxygenation and reoxygenation were 1.5-fold higher in the fit than the unfit volunteers. Differences in muscle deoxygenation, but not VO₂peak, were associated with gender-independent (p > 0.58) interaction effects between aerobic fitness × ACE-I/D genotype; being reflected in a 2-fold accelerated deoxygenation of VAS for aerobically fit than unfit ACE-II genotypes and a 2-fold higher deoxygenation of GAS for fit ACE-II genotypes than fit D-allele carriers.

Discussion: Aerobically fit subjects demonstrated increased rates of leg muscle deoxygenation and reoxygenation. Together with the higher muscle deoxygenation in aerobically fit ACE-II genotypes, this suggests that an ACE-I/D genotype-based personalization of training protocols might serve to best improve aerobic performance.

Keywords: aerobic metabolism; cycling; exhaustive pedaling; gene; oxygen saturation.

Figure 1

Representative example of the recorded SmO₂ course during the ramp test. Line graph visualizing the raw (gray) and processed data (black) and the derived parameters. SmO₂, muscle oxygen saturation; t, time; min, minimum; max, maximum. The extracted parameters are declared.

Figure 2

Oxygen saturation in VAS and GAS during the ramp test. Line graph visualizing the mean + SE (circle and vertical bars) of values for SmO₂ in VAS and GAS during the course of the ramp test. The three phases of the test are indicated. Values were averaged to each 9 s interval for the measures from the 34 subjects. The time coordinates for the values during the exercise phase were scaled for each subject to the duration of a reference data set.

Figure 3

Aerobic fitness state affects the kinetics of muscle oxygenation during exercise. Box Whisker plots (Box, 5 and 95% confidence intervals; Whisker, minima-maxima; central line, median; circle, individual values) for kinetic parameters of muscle deoxygenation (A–E) and reoxygenation (F–H) in VAS and GAS combined. Lines connect conditions demonstrating significant differences at p < 0.05. ANOVA for the factor “aerobic fitness” with post-hoc test of Fisher for the least significant difference.

Figure 4

Muscle deoxygenation during exercise is associated with the interaction between the aerobic fitness state and the angiotensin-converting enzyme-insertion/deletion (ACE-I/D) genotype. Box Whisker plots for the Δ_deoxgenation (A) and the slope of deoxygenation (B) in VAS and GAS combined in the function of the aerobic fitness status and the ACE-I/D genotype. Lines connect conditions demonstrating significant differences at *p < 0.05 and **p < 0.01. ANOVA for the factor “aerobic fitness” with post-hoc test of least significant difference.