Abstract 1050: Force-Endurance: A Novel Method to Assess Skeletal Muscle Training Effects in Heart Failure Patients
Purpose: Early muscular fatigue as one of the hallmarks of chronic heart failure (CHF) is not directly assessed by the exercise testing methods usually applied in CHF patients, which aim to measure integral cardiopulmonary exercise capacity (i.e. treadmill test, bicycle cardiopul-monary exercise test). To better quantify the effects of training interventions on muscular fatigue we used a novel two-step muscle force measurement protocol in stable patients with advanced CHF in two age groups (65 years), which were endurance-trained for four weeks.
Methods: 60 CHF-patients were randomized to 4 weeks of supervised bicycle ergometer training at 70% of the heart rate reserve 4 × 20 min/day or to a control group. Before and after the intervention a spiroergometry and a CT-scan at mid-thigh level to quantify muscle cross-sectional area (CSA) were performed. A Schnell M3 Diagnos system was used to measure quadriceps maximal contractile force at 90° knee angle. Maximal force endurance was assessed as the maximum time the patient was able to hold 50% of the individual isometric maximum.
Results: In younger CHF patients (n= 15, age 45±3 years, BMI 26.8±2.7, LV-EF 26.8±2.6%) training improved VO2 max by 36% from 13.3±1.6 to 18.1±1.5 mL/min kg (p=0.008 vs. control). Force endurance increased by 47% from 22.8±2.5 to 33.6±2.9 sec (p=0.002 vs. control). In elderly CHF patients (n=15, age 68±4 years, BMI 25.3±2.9, LV-EF 27.4±3.0%) the training intervention increased VO2 max by 33% from 12.9±1.4 to 17.1±1.1 mL/min kg (p=0.01 versus control). Force endurance improved by 44.2% from 23.5±4.2 to 33.9±4.1 sec (p=0.01 versus control, p=NS versus younger trained CHF patients). Maximal quadriceps force and muscle CSA remained unchanged in all patient groups.
Conclusions: Short-term endurance training does not only increase maximal exercise capacity as measured by ergospirometry in stable CHF patients, but also improves force endurance. These changes occur independently from changes in maximal muscle force or muscle cross-sectional area indicating that force endurance reflects metabolic changes in the skeletal muscle that may precede changes in muscle mass or contractile proteins. Training effects in force endurance were not attenuated in elderly CHF patients.