RESUMEN
BACKGROUND: Heart failure (HF) is the leading cause of death in western countries. Cardiac dysfunction is accompanied by skeletal alterations resulting in muscle weakness and fatigue. Exercise is an accepted interventional approach correcting cardiac and skeletal dysfunction, thereby improving mortality, re-hospitalization and quality of life. Animal models are used to characterize underpinning mechanisms. Transverse aortic constriction (TAC) results in cardiac pressure overload and finally HF. Whether exercise training improves cardiac remodeling and peripheral cachexia in the TAC mouse model was not analyzed yet. In this study, 2 weeks post TAC animals were randomized into two groups either performing a moderate exercise program (five times per week at 60% VO2 max for 40 min for a total of 8 weeks) or staying sedentary. RESULTS: In both TAC groups HF characteristics reduced ejection fraction (- 15% compared to sham, p < 0.001), cardiac remodeling (+ 22.5% cardiomyocyte cross sectional area compared to sham; p < 0.001) and coronary artery congestion (+ 34% diameter compared to sham; p = 0.008) were observed. Unexpectedly, peripheral cachexia was not detected. Furthermore, compared to sedentary group animals from the exercise group showed aggravated HF symptoms [heart area + 9% (p = 0.026), heart circumference + 7% (p = 0.002), right ventricular wall thickness - 30% (p = 0.003)] while muscle parameters were unchanged [Musculus soleus fiber diameter (p = 0.55), Musculus extensor digitorum longus contraction force (p = 0.90)]. CONCLUSION: The severe TAC model is inappropriate to study moderate exercise effects in HF with respect to cardiac and skeletal muscle improvements. Further, the phenotype induced by different TAC procedures should be well documented and taken into account when planning experiments.
Asunto(s)
Insuficiencia Cardíaca , Calidad de Vida , Animales , Modelos Animales de Enfermedad , Ventrículos Cardíacos , Ratones , Ratones Endogámicos C57BL , Músculo EsqueléticoRESUMEN
BACKGROUND: Heart failure (HF) is the leading cause of death in western countries. Cardiac dysfunction is accompanied by skeletal alterations resulting in muscle weakness and fatigue. Exercise is an accepted interventional approach correcting cardiac and skeletal dysfunction, thereby improving mortality, re-hospitalization and quality of life. Animal models are used to characterize underpinning mechanisms. Transverse aortic constriction (TAC) results in cardiac pressure overload and finally HF. Whether exercise training improves cardiac remodeling and peripheral cachexia in the TAC mouse model was not analyzed yet. In this study, 2 weeks post TAC animals were randomized into two groups either performing a moderate exercise program (five times per week at 60% VO2 max for 40 min for a total of 8 weeks) or staying sedentary. RESULTS: In both TAC groups HF characteristics reduced ejection fraction (- 15% compared to sham, p < 0.001), cardiac remodeling (+ 22.5% cardiomyocyte cross sectional area compared to sham; p < 0.001) and coronary artery congestion (+ 34% diameter compared to sham; p = 0.008) were observed. Unexpectedly, peripheral cachexia was not detected. Furthermore, compared to sedentary group animals from the exercise group showed aggravated HF symptoms [heart area + 9% (p = 0.026), heart circumference + 7% (p = 0.002), right ventricular wall thickness - 30% (p = 0.003)] while muscle parameters were unchanged [Musculus soleus fiber diameter (p = 0.55), Musculus extensor digitorum longus contraction force (p = 0.90)]. CONCLUSION: The severe TAC model is inappropriate to study moderate exercise effects in HF with respect to cardiac and skeletal muscle improvements. Further, the phenotype induced by different TAC procedures should be well documented and taken into account when planning experiments.
Asunto(s)
Animales , Ratones , Calidad de Vida , Insuficiencia Cardíaca , Músculo Esquelético , Modelos Animales de Enfermedad , Ventrículos Cardíacos , Ratones Endogámicos C57BLRESUMEN
We hypothesized that prior exercise would attenuate the muscle fatigue accompanied by oxygen uptake slow-component (VÌO2SC) behavior during a subsequent very-heavy (VH)-intensity cycling exercise. Thirteen healthy male subjects performed tests to determine the critical power (CP) and the fixed amount of work above CP ([Formula: see text]) and performed 6 square-wave bouts until 3 or 8 min, each at a work rate set to deplete 70% [Formula: see text] in 8 min, with a maximal isokinetic effort before and after the conditions without (VHCON) and with prior exercise (VHEXP), to measure the cycling peak torque decrement. The VÌO2SC magnitude at 3 min (VHCON = 0.280 ± 0.234, VHEXP = 0.116 ± 0.109 L·min-1; p = 0.04) and the VÌO2SC trajectory were significantly lower for VHEXP (VHCON = 0.108 ± 0.042, VHEXP = 0.063 ± 0.031 L·min-2; p < 0.01), leading to a VÌO2SC magnitude at the eighth minute that was significantly lower than VHCON (VHCON = 0.626 ± 0.296 L·min-1, VHEXP = 0.337 ± 0.179; p < 0.01). Conversely, peak torque progressively decreased from pre-exercise to 3 min (Δtorque = 21.5 ± 7.7 vs. 19.6 ± 9.2 Nm) and to 8 min (Δtorque = 29.4 ± 15.8 vs. 27.5 ± 12.0 Nm) at VHCON and VHEXP, respectively, without significant differences between conditions. Regardless of the condition, there was a significant relationship between Δtorque and the VÌO2SC (R2: VHCON = 0.23, VHEXP = 0.25; p = 0.01). Considering that "priming" effects on the VÌO2SC were not accompanied by the muscle force behavior, these findings do not support the hypothesis of a "causal" relationship between the time-course of muscle fatigue and VÌO2SC.
Asunto(s)
Ciclismo/fisiología , Ejercicio Físico/fisiología , Fatiga Muscular , Consumo de Oxígeno , Adulto , Humanos , Masculino , Músculo Esquelético/fisiología , Torque , Adulto JovenRESUMEN
INTRODUCTION: The purpose of this study was to examine the acute effect of different rest intervals between multiple sets of the 45° angled leg press exercise (LP45) on surface electromyographic (SEMG) spectral and amplitude indices of fatigue. METHODS: Fifteen recreationally trained females performed three protocols in a randomized crossover design; each consisting of four sets of 10 repetitions with 1 (P1), 3 (P3), or 5 (P5) minute rest intervals between sets. Each set was performed with 70% of the LP45 ten-repetition maximum load. The SEMG data for biceps femoris (BF), vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles was then evaluated. RESULTS: The SEMG amplitude change in the time coefficient (CRMS) and spectral fatigue index (Cf5) indicated higher levels of fatigue for all muscles evaluated during the P3 protocol versus the P1 and P5 protocols (p ≤ 0.05), respectively. The RF and VL muscles showed greater fatigue levels by the second and third sets; whereas, greater fatigue was shown in the VM and BF muscles by the fourth set (p ≤ 0.05). CONCLUSIONS: A three-minute rest interval between sets might represent a neuromuscular window between a fatigue stated and fully recovered state in the context of neural activation. Moreover, a three minute rest interval between sets might allow for consistent recruitment of high threshold motor units over multiple sets, and thus promote a more effective stimulus for strength gains.