Aspectos neuromusculares e biodinâmicos relacionados à idade nos membros superiores e inferiores de mulheres

Abstract

Aging is a multifactorial process that causes changes in the quantity and quality of skeletal muscle. Muscle atrophy, along with functional impairment, is associated with an impaired state of health with high personal losses. Studies have shown that the ability to generate force quickly may be more functionally relevant than the capacity of maximum force, since many of the activities of daily life are characterized by limited time of force development (50-200ms), which is considerably less than that required to achieve maximum force (≥ 300ms). However, the age-related changes do not occur evenly among muscle groups. Based on the lack of studies which analyze the neuromuscular and biodynamic aspects in the superior and lower limbs in related to age women, which are characterized by having the highest rates of disability and longevity, this study aimed to investigate in women of distinct age group: whether the strength, the fat-free mass (FFM) and the power of the electromyography signal of upper and lower limbs are affected in the same magnitude by aging (Study 1) and age-related changes in the temporal development of force of handgrip and knee extensors (study 2). In the first study, we analyzed the maximal isometric strength of handgrip and knee extension, the power of the electromyography signal of the flexor muscles of the hand and the vastus lateralis through the root mean square variable normalized by the FFM of the dominant limb (RMSn) and the FFM by Dual-energy Xray absorptiometry in 63 women, subdivided in three groups (JO. n=33, 24.7±3.5 years; MI. n=15, 58.6±4.2 years; ID. n=15, 72.0±4.2 years). The handgrip strength was similar among groups (p=0,523), the FFM of the upper limb was lower in group ID in compared JO (p=0.108) and the RMSn values of the hand flexors was similar among groups (p=0.754). However, the strength of the knee extensors, the FFM of the lower limb and the RMSn values of the vastus lateralis were lower in group MI (p=0.014, p=0.006 e p=0.013, respectively) and ID (p=0.000, p=0.000 e p<0.000, respectively) in compared JO. In Study 2, we assessed the FFM, maximal isometric strength of handgrip and knee extension and the temporal development of force during those tests in 52 women, subdivided in three groups (JO. n=24, 25.2±3.7 years; MI. n=13, 58±4.2 years; ID. n=15, 71.3±3.9 years). Values were similar in strength (p=0.831) and FFM (p=0.207) of the upper limb. The rate of force development (RFD) was lower in the initial periods of muscle contraction (0-50 and 0- 100ms) in the MI group (p=0.005 and p=0.000 for 50ms and 100ms, respectively) and ID (p=0.003 p=0.000 for 50ms and 100ms, respectively). The FFM and lower limb strength was lower in the MI group (p=0.006, p =0.014, respectively) and ID (p<0.000, p=0.000, respectively) compared to the JO. Already the RFD of the knee extensors was similar in the MI group (p>0.05), but lower in the ID group (p<0.05) compared to the JO in all analyzed intervals. According to the results of Studies 1 and 2, the lower limbs are most affected by the aging process. Thus, it is necessary to develop a strategy of adequate training for elderly and middle-aged women, especially for the lower limbs, in order to maintain function and quality of life for this population.