Nicoletta Rinaldo

Muscle fiber conduction velocity and fractal dimension of EMG during fatiguing contraction of young and elderly active men.

Over the past decade, linear and nonlinear surface electromyography (EMG) variables highlighting different components of fatigue have been developed. In this study, we tested fractal dimension (FD) and conduction velocity (CV) rate of changes as descriptors, respectively, of motor unit synchronization and peripheral manifestations of fatigue. Sixteen elderly (69  ±  4 years) and seventeen young (23  ±  2 years) physically active men (almost 3-5 h of physical activity per week) executed one knee extensor contraction at 70% of a maximal voluntary contraction for 30 s. Muscle fiber CV and FD were calculated from the multichannel surface EMG signal recorded from the vastus lateralis and medialis muscles. The main findings were that the two groups showed a similar rate of change of CV, whereas FD rate of change was higher in the young than in the elderly group. The trends were the same for both muscles. CV findings highlighted a non-different extent of peripheral manifestations of fatigue between groups. Nevertheless, FD rate of change was found to be steeper in the elderly than in the young, suggesting a greater increase in motor unit synchronization with ageing. These findings suggest that FD analysis could be used as a complementary variable providing further information on central mechanisms with respect to CV in fatiguing contractions.

Severe COPD Alters Muscle Fiber Conduction Velocity During Knee Extensors Fatiguing Contraction

Abstract The aim of this study was to assess the changes in muscle fiber conduction velocity (CV), as a sign of fatigue during knee extensor contraction in patients with chronic obstructive pulmonary disease (COPD) as compared with healthy controls. Eleven male patients (5 with severe and 6 with moderate COPD; age 67 ± 5 years) and 11 age-matched healthy male controls (age 65 ± 4 years) volunteered for the study. CV was obtained by multichannel surface electromyography (EMG) from the vastus lateralis (VL) and medialis (VM) of the quadriceps muscle during isometric, 30-second duration knee extension at 70% of maximal voluntary contraction. The decline in CV in both the VL and VM was steeper in the severe COPD patients than in healthy controls (for VL: severe COPD vs. controls −0.45 ± 0.07%/s; p < 0.001, and for VM: severe COPD vs. controls −0.54 ± 0.09%/s, p < 0.001). No difference in CV decline was found between the moderate COPD patients and the healthy controls. These findings suggest that severe COPD may impair muscle functions, leading to greater muscular fatigue, as expressed by CV changes. The results may be due to a greater involvement of anaerobic metabolism and a shift towards fatigable type II fibers in the muscle composition of the severe COPD patients.

Electromyographic Manifestations of Fatigue Correlate With Pulmonary Function, 6-Minute Walk Test, and Time to Exhaustion in COPD

BACKGROUND: The aim of this study was to investigate whether electromyographic manifestations of fatigue and exercise tolerance were related to stage of disease in men with a COPD diagnosis. METHODS: Fourteen men with COPD with a diagnosis of mild to severe air flow obstruction were involved in 2 separate testing sessions. The first one consisted of a pulmonary function (FEV1 and FEV1/FVC) and an exercise tolerance assessment using the 6-min walk test. During the second session, a multichannel surface electromyography was recorded from vastus medialis and vastus lateralis muscles during an isometric knee extension at 70% of maximum voluntary contraction. The slope of muscle fiber conduction velocity during the contraction was calculated as the index of fatigue. RESULTS: Conduction velocity slope significantly correlated with FEV1 (vastus medialis: r = 0.86, P < .001; vastus lateralis: r = 0.68, P = .01), FEV1/FVC (vastus medialis: r = 0.70, P = .006), and 6-min walk test (vastus medialis: r = 0.72, P = .005; vastus lateralis: r = 0.80, P = .001). CONCLUSIONS: The electromyographic manifestations of fatigue during sustained quadriceps contraction significantly correlated with disease severity and exercise tolerance in moderate to severe COPD.

Differences in age-related fiber atrophy between vastii muscles of active subjects: a multichannel surface EMG study

The aim of the study was to non-invasively determine if vastus lateralis (VL) and vastus medialis obliquus (VM) muscles are equally affected by age-related fiber atrophy. Multichannel surface electromyography was used since it allows to estimate muscle fiber conduction velocity (CV), which has been demonstrated to be related to the size of recruited muscle fibers. Twelve active elderly men (age 69   ±   4 years) and 12 active young men (age 23   ±   2 years) performed isometric knee extension at 30%, 50%, and 70% of maximal voluntary contraction. Electromyographic signals were recorded from VL and VM muscles of the dominant limb using arrays with eight electrodes and CVs were estimated for each contraction. CV estimates showed a different behavior in the two muscles: in VL at 50% and 70% of maximum voluntary contraction they were greater in young than in elderly; whereas such a difference was not observed in VM. This finding suggest that in active elderly VM seems to be less affected by the age-related fibers atrophy than VL. Hence, the common choice of studying VL as a muscle representative of the whole quadriceps could generate misleading findings. Indeed, it seemed that the sarcopenic ageing effects might be heterogeneous within quadriceps muscle.

Effects of Combined Aerobic-Strength Training vs Fitness Education Program in COPD Patients

We compared the effects of a new physical activity education program approach (EDU), based on a periodically supervised protocol of different exercise modalities vs traditionally supervised combined strength-endurance training (CT) on health-related factors in patients with stable chronic obstructive pulmonary disease (COPD). Twenty-eight COPD patients without comorbidities were randomly assigned to receive either EDU or CT. CT was continuously supervised to combine strength-endurance training; EDU was taught to progressively increase the rate of autonomous physical activity, through different training modalities such as Nordic walking, group classes and circuit training. Body composition, walking capacity, muscle strength, flexibility and balance, total daily energy expenditure and quality of life were evaluated at baseline, after 28 weeks training period (3d/week) and after a 14-week follow-up. No adverse events occurred during the interventions. After training, CT and EDU similarly improved walking capacity, body composition and quality of life. However, after 14 weeks of follow-up, such improvements were not maintained. Only in CT, muscle strength and flexibility improved after training but returned to baseline after follow-up. EDU, similar to CT, can effectively and safely improve health-related parameters in COPD patients. EDU could be an attractive alternative to traditional supervised training for improving quality of life in COPD patients.

Quadriceps concentric-eccentric force and muscle architecture in COPD patients vs healthy men

The aim of this study was to compare quadriceps concentric and eccentric strength and muscle architecture in chronic obstructive pulmonary disease (COPD) patients vs healthy men. Thirty-five COPD patients (age = 65 ± 4 yrs, forced expiratory volume (FEV1) = 63 ± 10%; FEV1/forced vital capacity (FVC)=57 ± 13% of predicted) and 25 age-matched healthy men (age = 65 ± 4 yrs, FEV1=114 ± 17%; FEV1/FVC = 101 ± 6% of predicted) (CON) participated in the present cross-sectional study. Concentric and eccentric isokinetic peak-torque was measured at low and high angular-velocity. Vastus lateralis pennation angle, fascicle length and muscle thickness were recorded using ultrasound device. Similar eccentric peak-torque was found in COPD and CON at low (2.57 ± 0.55 and 2.80 ± 0.60 N⋅m⋅kg-1, p = 0.128 respectively) and high (2.44 ± 0.51 and 2.58 ± 0.46 N⋅m⋅kg-1, p = 0.259) angular-velocity. Lower concentric peak-torque was found in COPD than in CON (p < 0.05). Smaller pennation angle (13.8 ± 3.4 vs 16.2 ± 3.9°) and muscle thickness (17.1 ± 2.8 vs 20.3 ± 3.0 mm) were found in COPD patients vs healthy men, with no difference in fascicle length. In COPD patients only, FEV1 and FEV1/FVC were negatively correlated with the eccentric-to-concentric peak-torque ratio (r = -0.465 and r = -0.414, respectively); irrespective of the testing-modality, FEV1 and FEV1/FVC were moderately correlated with peak-torque (p < 0.05). The preserved eccentric strength in COPD patients could be accounted for both mechanical and neural adaptations caused by the disease severity.