Effects of 12-Week Home-based Resistance Training on Peripheral Muscle Oxygenation in Children With Congenital Heart Disease: A CHAMPS Study

Figure 1. Flow diagram of the study design for participants with CHD. “Insufficient peak test” indicates that participants did not meet the criteria for a “good effort” test as per an RER >0.90. CHD, congenital heart disease; HR, heart rate; RER, respiratory exchange ratio; TOI; tissue oxygenation index.

Figure 2. Flow diagram of the study design for CTL participants. CTL, control; HR, heart rate.

Figure 3. Representative data illustrating total labile signal (TLS) calibration. Tissue oxygenation index (TOI) is scaled from the nonexercising baseline value (100% TOI) to the value during ischemia from femoral cuff inflation above systolic pressure (0% TOI).

Figure 4. (A) TOI and (B) V˙O2 reserve in children with CHD compared with CTL at peak exercise. Data points are individual data. The red line is the group mean. Comparisons were made using multiple 2-tailed t-tests with the Holm-Šídák correction for multiple comparisons. Cohen’s d effect size analysis was completed for pre- to post-testing in CHD, where a small effect is ≥0.20, a medium effect is ≥0.50, and a large effect is ≥0.80. CHD, congenital heart disease; CTL, control; Pre, pre-exercise training; Post, post-exercise training; TOI, tissue oxygenation index.

Figure 5. Depiction of the main study findings. The illustration indicates physiological responses during exercise before (left) and after (right) home-based resistance training. There was a small effect of training on lowering heart rate at peak exercise after training. It is also hypothesized that there was also no increase in the limb blood flow (and “bulk” oxygen delivery) during exercise from before to after training. There was a medium effect of exercise training on decreasing TOI (tissue oxygenation index) at peak exercise that is hypothesized to occur secondary to an increase in skeletal muscle capillarity and/or muscle metabolism. The increase in capillary density would subsequently slow the flux of red blood cells across the muscle bed, thus facilitating greater time for potential diffusion of oxygen to the mitochondria. Greater metabolic activity and/or number of mitochondria after training facilitates greater oxygen extraction from blood and effectively increases the arterial-venous oxygen content difference and is noted by a lower TOI value. By way of the Fick equation where V˙O2 = cardiac output × arterial-venous oxygen content difference, the small effect of exercise…