**4. Performance in daily activities**

Thus, we can see that age-related muscle strength loss decreases maximal joint torque and power production, yet the muscle activation mechanisms that promote this behavior are still

Despite is expected a reduced fatigability in older adults, the findings of several studies is

During muscular fatigue, there are changes in the amplitude and frequency of the EMG signal (Cardozo & Gonçalves, 2003, Cardozo et al., 2011), which is dependent on the number of active motor units, their firing rates and the conduction velocity (Oliveira & Gonçalves, 2009). These changes are described in figure 2. Along these lines, EMG is widely used to highlight the muscular fatigue phenomenon in several populations, including people who suffer from back pain, athletes and, recently, older adults (Croscato et al., 2011, Fraga et al., 2011, Hunter et al.,

**Figure 2.** Amplitude (root mean square-RMS) and frequency (median frequency) behavior due to an isometric fatigu‐

Hunter et al. (2004) compared the time to task failure, physiological responses (mean arterial pressure, heart rate, and rating of perceived exertion) and EMG responses at a sustained submaximal isometric contraction (20% of MVC) for elbow flexion in young and old men and women. The main finding of this study was that the time to task failure was longer with older adults, regardless of gender, and longer with young women than with young men. However, older adults had a reduced rate of increase in physiological parameters (mean arterial pressure,

not well described.

2004, Lindström et al., 2006).

ing protocol (Cardozo et al., unpublished data).

**3. Muscles activation and fatigability**

116 Electrodiagnosis in New Frontiers of Clinical Research

controversial (Allman & Rice, 2002, Avin & Frey Law, 2011).

Everyday tasks are motor acts performed during a day that contribute to physical independ‐ ence, such as rising from a seated position, ascending or descending stairs, walking and taking a shower. Challenges encountered during daily activities, which are easily overcome by young adults, may represent a potential risk for falls among the elderly. Functional motor activities are especially difficult for older adults due to sensorimotor deficits related to age, exposing these older adults to fatal accidents and serious injuries (Korteling, 1994, Roeneker et al., 2003).

Stair descent and ascent are also important functional abilities (Holsgaard et al., 2011). Studies indicate that the elderly operated at a higher proportion of their maximal capacity than did young adults when performing tasks such as the safe descent of stairs (Reeves et al., 2008). Hinman et al. (2005) used EMG to record muscle activity during stair descent. They determined the effects of age on the onset of vastus medialis obliquus activity relative to that of vastus lateralis and the onset of quadriceps activity in the terminal swing relative to heel-strike during stair descent. Muscle onset was identified from individual EMG traces with a computer algorithm and was validated visually. The results show that older adults activated their quadriceps significantly earlier than the younger group during stair descent. Thus, quadricep activation may compensate for strength and balance impairments in older people during

Age-Related Neuromuscular Adjustments Assessed by EMG

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

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Dexterous manipulations, such as eating and writing, may deteriorate due to aging (Keogh et al., 2007). Reduced hand function is related to the loss of finger-pinch force control (Keogh et al., 2006, Lazarus & Haynes, 1997, Ranganathan et al., 2001). Keogh et al. (2007) determined the effect of unilateral upper-limb strength training on the finger-pinch force control of older men by EMG. The EMG activity of the flexor pollicis brevis and flexor digitorum superficialis muscles was recorded using a sample rate of 1000 Hz, and the EMG data were subsequently filtered with a second-order Butterworth low-pass filter with the cutoff frequency set at 400 Hz. The amplitude of the electromyographic signals was obtained by using the RMS procedure with a bin size of 100 ms. The results show that a nonspecific upper-limb strength-training program may improve the finger-pinch force control of older men. However, additional studies are required to create strategies for the

The capacity to maintain the body in an upright position in a stable state is critical to prevent falls in old people. This capacity requires the integration of visual feedback, the vestibular system, proprioception, reaction times and muscular responses. However, these mechanisms are negatively affected by aging, and therefore, the adaptive reflexes that respond to distur‐ bances of balance are damaged (Abreu & Caldas, 2008). As a result of these changes, the elderly

EMG can evaluate the response of muscles during postural control in different situations requiring the integrity of the neuromuscular system. Figure 3 presents the time delay between a perturbation (accelerometer signal) and the muscle activation (EMG onset) response obtained by EMG analyses of the tibialis anterior muscle. This time delay is negatively affected by the aging process, promoting slower responses in old adults. This behavior may increase the risk of falls in this population when the muscle activation may not be fast enough to maintain

improvement of hand-held movements in older adults.

**5. Changes in postural control**

become more prone to falls (Tinetti, 2003).

stability after a perturbation.

challenging activities.

An age-related decline in the ability to perform physical tasks associated with daily living as well as in strength and muscle size may occur regardless of physical fitness or amount of training (Klitgaard et al., 1990, Schulz & Curnow, 1998). The decline in force and task per‐ formance may be related to alterations in the activation of motor units, decreases in muscle mass and increases in fat mass (Lexell, 1995).

Performance in daily tasks may be investigated by EMG in young and old persons. A study performed by Landers et al. (2001) analyzed integrated electromyography (IEMG) in two tasks of daily living: while the subjects sat down on a chair and while they carried a small load. The muscles analyzed were rectus femoris and biceps brachii. The raw EMG signal was recorded over six seconds for each collection point at a sample rate of 100 Hz. Subjects were given three practice trials, followed by three maximum isometric contractions at each test angle. The results showed that higher normalized integrated EMG values indicate greater muscular effort and, when combined with other tests, that biomechanical measures can provide information about muscle function in older adults.

The ability to walk efficiently and safely is important to maintain independence (Callisaya et al., 2010). However, the energy cost of gait in the elderly is higher than in young people, which can cause early fatigue (Hortobagyi et al., 2009). However, little is known about what makes the elderly more prone to fatigue during the gait, but existing hypotheses are that this fatigue is related to neuromuscular mechanisms, such as increased muscle coactivation (Burnett et. al., 2000, Hortobagyi et al., 2009, Macaluso et al., 2002). Increased coactivation might be used to optimize power generation and compensate for aging-related decline of neuromotor functioning, as manifested by reduced strength and power of muscles, reduced proportions of fast twitch muscle fibers and increased response times (Ishida et al., 2008).

Older adults also require greater effort relative to their available maximal capacity to execute daily motor tasks when compared with younger adults (Hortobagyi et al., 2003). This is due to a change in muscle fiber type with aging and a higher percentage of peak oxygen uptake required to perform daily tasks (Astrand et al., 1973, Waters et al., 1983). Higher physiological relative effort in elderly people may be the cause of premature fatigue associated with decline of motor function and, consequently, falls. Hortobagyi et al. (2003) tested the hypothesis that the relative effort to execute daily activities is higher in old adults compared with young adults. They assessed the vastus lateralis and biceps femoris muscles by EMG during the ascent and descent of stairs, the rise from a chair and the performance of maximal-effort isometric supine leg presses. The EMG signals were sampled at 1000 Hz, and the dependent variables included the average root mean square (RMS) EMG and EMG coactivity, expressed as a ratio of biceps femoris root mean square EMG with vastus lateralis RMS EMG activity. The results show that the relative vastus lateralis EMG activity is higher in old adults than young adults during some daily activities, and an association exists between the increased relative effort at the knee joint and increased muscle activation.

Stair descent and ascent are also important functional abilities (Holsgaard et al., 2011). Studies indicate that the elderly operated at a higher proportion of their maximal capacity than did young adults when performing tasks such as the safe descent of stairs (Reeves et al., 2008). Hinman et al. (2005) used EMG to record muscle activity during stair descent. They determined the effects of age on the onset of vastus medialis obliquus activity relative to that of vastus lateralis and the onset of quadriceps activity in the terminal swing relative to heel-strike during stair descent. Muscle onset was identified from individual EMG traces with a computer algorithm and was validated visually. The results show that older adults activated their quadriceps significantly earlier than the younger group during stair descent. Thus, quadricep activation may compensate for strength and balance impairments in older people during challenging activities.

Dexterous manipulations, such as eating and writing, may deteriorate due to aging (Keogh et al., 2007). Reduced hand function is related to the loss of finger-pinch force control (Keogh et al., 2006, Lazarus & Haynes, 1997, Ranganathan et al., 2001). Keogh et al. (2007) determined the effect of unilateral upper-limb strength training on the finger-pinch force control of older men by EMG. The EMG activity of the flexor pollicis brevis and flexor digitorum superficialis muscles was recorded using a sample rate of 1000 Hz, and the EMG data were subsequently filtered with a second-order Butterworth low-pass filter with the cutoff frequency set at 400 Hz. The amplitude of the electromyographic signals was obtained by using the RMS procedure with a bin size of 100 ms. The results show that a nonspecific upper-limb strength-training program may improve the finger-pinch force control of older men. However, additional studies are required to create strategies for the improvement of hand-held movements in older adults.
