**6. Effects of physical activity on the neuromuscular system**

Decreases in maximal isometric, concentric, and eccentric forces, force development rate and muscle power are all age-related effects (Granacher et al., 2010, Petrella et al., 2005, Skelton et al., 1994). Regular physical exercise for the elderly population has been identified as an important intervention in the treatment and recovery of some diseases (Bassey, 1997). As the functional benefit of exercise may be greatest in older adults, in recent years, there have been several studies about the effects of physical activity on the neuromuscular system of this population.

Traditional strength training protocols can still be recommended to improve muscle strength and voluntary neural activity in older adults (Fung & Hughey, 2005, Runge et. al., 1998). However, other types of training have been shown to develop strength, power and balance in this population. Resistance training with power training and ballistic strength training may be effective for improving explosive force production and functional performance in old age (Granacher et al., 2011). Orr et al. (2006) show that power training at low intensities can improve balance, power, strength and endurance in the lower limb muscles of older adults. Recent studies have also shown that whole body vibration and resistance exercises combined with vascular occlusion may improve muscle strength (Granacher et al., 2012, Rabert et al., 2011, Takarada et al., 2000). Figure 4 shows the influence of an active lifestyle on increasing healthy life expectancy.

The assessment of lower limb muscle activity provides important information about neuro‐ muscular behavior before and after physical activities (Schmitz et al., 2009). EMG can identify changes in the motor skills of older adults and help create prevention strategies for ageassociated changes in neuromuscular factors that can impair daily activities and increase the rate of falls among this population.

**Figure 3.** EMG response due to perturbation (Cardozo et al., unpublished data).

longer than younger adults.

120 Electrodiagnosis in New Frontiers of Clinical Research

ces (Pijnappels et al., 2008).

Older people have different strategies to maintain posture in balance situations: the ankle strategy responds to slow disturbances; the hip strategy is used on larger and faster displace‐ ments of the center of pressure (COP); and the step strategy is used when the others are not able to return the COP to the support base, using quick jumps or steps (Vanicek et al., 2009).

Another strategy used by older adults is an increase in antagonistic muscle activation during balance recovery (Mixco et al., 2012). This coactivation can be a necessary change to compensate for the decline in postural control associated with aging (Nagai et al., 2011). Additionally, Freitas et al. (2009) have shown that older adults activated their muscles and were able to reach the peak of activation. However, they retained a higher level of activation

As a result of the aging process, reaction time tends to increase due to the atrophy of fast twitch fibers with aging. This atrophy contributes to a lower power output, slower sensory feedback and slower muscle onset, resulting in ineffectiveness of equilibrium recovery after disturban‐

Due to physiological changes resulting from the aging process, recovery strategies are slower and therefore less effective in old adults (Mian et al., 2007). Thus, to minimize these changes, physical activity is highly recommended and widely used as an intervention to prevent falls.

A recent study investigated the effects of strength and endurance exercises over the course of 12 weeks in older adults. The maximal neuromuscular activity of agonist muscles was evaluated using EMG (RMS) in the vastus lateralis and rectus femoris and antagonist coactivation in the biceps femoris long head. The sampling frequency was 2000 Hz, and the data were filtered using a Butterworth band-pass filter of the fourth order with a cutoff frequency between 20 and 500 Hz. The RMS values of the antagonist biceps femoris muscle were normalized by the maximum RMS values of this muscle. After determination of the maximal neuromuscular activity, the submaximal neuromuscular activity was evaluated to determine the isometric neuromuscular economy. The results show that training in older adults resulted in greater changes in neuromuscular economy as assessed by EMG (Cardore et al., 2012). Similarly, Cardore et al. (2011) investigated the effects of concurrent training on endurance capacity and dynamic neuromuscular economy in elderly men. During the maximal test, muscle activation was measured at each intensity by means of electromyographic signals from the vastus lateralis, rectus femoris, biceps femoris long head, and gastrocnemius lateralis to determine the dynamic neuromuscular economy. Changes in the myoelectric activity of the Rectus Femoris and Vastus Lateralis muscles were observed as an adaptative response after strength and endurance training.

pattern providing a recruitment pattern (Hakkinen et al., 1998, Hakkinen et al., 2001, Ling et al., 2009). Additionally, the EMG changes can also be related to reduced antagonist muscle coactivation (Hakkinen et al., 2001). This phenomenon may enhance the agonists' force production, which is important in older adults during multijoint actions (Hakkinen et al., 1998). Furthermore, the maintenance of balance during daily activities may represent a challenge for older adults (Bugnariu & Fung, 2007). Aging is also associated with a decrease in the ability to control the body's position, requiring input from the afferent receptor systems to generate an appropriate motor response in dynamic and static activities (Alexander, 1994, Granacher et al., 2012, Woollacott & Shumway-Cook, 2002). Due to age-related decline in the integrity of many postural regulating systems, rehabilitation is needed to promote the re-acquisition of motor skills (Maki & Mcllroy, 1996). Along these lines, physical exercise is the most common intervention to prevent the consequences of balance perturbations, such as falls, fractures and

Age-Related Neuromuscular Adjustments Assessed by EMG

http://dx.doi.org/10.5772/55053

123

To improve balance, physical activity protocols include progressively difficult postures that reduce the base of support as well as dynamic movements that perturb the center of gravity, stress postural muscle groups and reduce sensory input (Granacher et al., 2012). In addition, multisensory exercises that stimulate all three afferent systems can be a good strategy for intervention (Alfieri et al., 2010, Bruin & Murer, 2007, Nitz & Choy, 2004, Orr et al., 2008;). Bugnariu & Fung (2007) investigated the effects of aging and adaptation on the capability of the central nervous system to select pertinent sensory information and resolve sensory conflicts. EMG activity was collected from the tibialis anterior, gastrocnemius medialis, vastus lateralis, semitendinosus, tensor fascia lata, erector spinae, neck extensor and neck flexor sternocleidomastoideus. Functional balance and mobility were assessed before and after virtual environment exposure and perturbation trials. The group found that after exposure to sensory conflicts, the central nervous system can adapt to the changes and improve balance

This chapter presents a global understanding of age-related neuromuscular alterations, such as weakness and fatigue, and the use of EMG parameters in their identification. Neuromus‐ cular adaptations due to aging influence the ability of the elderly to maintain the capacity to perform daily activities and to modulate their postural control. Additionally, physical activity

The authors would like to thank the Biomechanics Laboratory of the Department of Physical Education (Instituto de Biociências de Rio Claro, UNESP – Univ Estadual Paulista) and the

can improve neuromuscular functional ability in older people.

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).

death (Alfieri et al., 2012, Morey et al., 2008).

capability in the elderly.

**Acknowledgements**

**7. Conclusion**

**Figure 4.** An active lifestyle enhances physical activity and decreases sedentary behaviors (Cardozo et al., unpublished data).

Valkeinen et al. (2006) examined the EMG activity after a 21 week strength training period in elderly woman with fibromyalgia. The EMG activity of the right vastus lateralis and vastus medialis muscles was recorded during maximal isometric leg extensions, and the results were expressed as the mean integrated EMG activity. There was a large increase in the maximal force and EMG activity of the muscles, indicating that strength training for elderly people can increase neuromuscular functional performance. Hakkinen et al. (2001) examined neuromus‐ cular adaptations in middle-aged and older men and women during a resistance training period of 6 months. The EMG activity during the unilateral extension actions of the knee muscles was recorded from the agonist muscles vastus lateralis and vastus medialis and from the biceps femoris. The EMG signal was collected at 1000Hz, full wave rectified and integrated. The results show that there were increases in the EMG integrated magnitude of the agonist muscle during isometric and concentric leg extensions at maximal voluntary contraction in older women after training. This finding may be related to changes in the muscle activation pattern providing a recruitment pattern (Hakkinen et al., 1998, Hakkinen et al., 2001, Ling et al., 2009). Additionally, the EMG changes can also be related to reduced antagonist muscle coactivation (Hakkinen et al., 2001). This phenomenon may enhance the agonists' force production, which is important in older adults during multijoint actions (Hakkinen et al., 1998).

Furthermore, the maintenance of balance during daily activities may represent a challenge for older adults (Bugnariu & Fung, 2007). Aging is also associated with a decrease in the ability to control the body's position, requiring input from the afferent receptor systems to generate an appropriate motor response in dynamic and static activities (Alexander, 1994, Granacher et al., 2012, Woollacott & Shumway-Cook, 2002). Due to age-related decline in the integrity of many postural regulating systems, rehabilitation is needed to promote the re-acquisition of motor skills (Maki & Mcllroy, 1996). Along these lines, physical exercise is the most common intervention to prevent the consequences of balance perturbations, such as falls, fractures and death (Alfieri et al., 2012, Morey et al., 2008).

To improve balance, physical activity protocols include progressively difficult postures that reduce the base of support as well as dynamic movements that perturb the center of gravity, stress postural muscle groups and reduce sensory input (Granacher et al., 2012). In addition, multisensory exercises that stimulate all three afferent systems can be a good strategy for intervention (Alfieri et al., 2010, Bruin & Murer, 2007, Nitz & Choy, 2004, Orr et al., 2008;). Bugnariu & Fung (2007) investigated the effects of aging and adaptation on the capability of the central nervous system to select pertinent sensory information and resolve sensory conflicts. EMG activity was collected from the tibialis anterior, gastrocnemius medialis, vastus lateralis, semitendinosus, tensor fascia lata, erector spinae, neck extensor and neck flexor sternocleidomastoideus. Functional balance and mobility were assessed before and after virtual environment exposure and perturbation trials. The group found that after exposure to sensory conflicts, the central nervous system can adapt to the changes and improve balance capability in the elderly.
