Large Vs Small Skeletal Muscle Mass Training: A Study On Solid Organ Transplanted Recipients

Abstract

Heart, kidney and liver transplanted patiences (HTR, KTR and LTR) suffer from a reduced exercise capacity. Several studies pointed out the impairments of both central and peripheral factors as responsible for the decreased peak oxygen consumption (V’O2peak) and diminished peak work rate (WRpeak); however, if the main limitation comes from central or peripheral origin is still unclear (Williams and McKenna, 2012). In healthy humans, V’O2peak is mainly constrained by central factors with peripheral factors playing a minor role, indeed endurance training (ET) involving small muscle mass fails to increase whole-body V’O2peak (Rud et al, 2012). Given the skeletal muscle abnormalities reported in HTR, KTR and LTR the limitation conferred by peripheral factors might be important as the central one. PURPOSE: The study investigated if ET of small muscle mass, e.g. single leg cycling (SL), induces higher increase in V’O2peak and WRpeak than ET with large muscle masses, e.g. double leg cycling (DL), in HTR, KTR and LTR. METHODS: 33 sedentary patience were enrolled and divided into SL group (SLG) (n= 17; HTR=6, KTR=6 and LTR=5) and DL (DLG) (n= 16; HTR=7, KTR=5 and LTR=4). Subjects completed DL incremental tests to determine V’O2peak and WRpeak; peak cardiac output (Q’peak) was assessed by cardio-impedance and peak systemic arterio-venous O2 difference (Ca-vO2peak) was calculated as: V’O2peak/Q’peak. All subjects were asked to attend 24 ET sessions: the DLG performed traditional cycling and the SLG the first half of the session with the one leg and the second half with the other limb. RESULTS: SLG and DLG increased V’O2peak by 19.7 ± 2.7% (mean ± SE) and 23.2 ± 3.1% (Time effect: P<0.001), respectively; WRpeak became 15.3 ± 2.2% and 18.2 ±3.2% larger in SLG and DLG (Time effect: P<0.001), respectively. Q’peak changed by -1.5 ± 5.5% in SLG (n=11) and by 6.7 ± 5.3% in DLG (n=10), however no effect of ET was found Q’peak. Ca-vO2peak improved by 17.6 ± 6.5% and 12.7 ± 6.2% in SLG (n=11) and DLG (n=10) (Time effect: P: 0.003), respectively. CONCLUSIONS: Given the absence of improvement in Q’peak after ET, the accretion of V’O2peak and WRpeak seems to be induced by a greater Ca-vO2peak, suggesting a key role of peripheral factors in impairing exercise capacity in HTR, KTR and LTR.