Age related changes in muscle system are directly related to limited mobility and increase of falls in the elderly. Aging is associated with decrease in total muscle cross-sectioned area amounting to approx 40% between the ages of 20 and 80 years. Cummingham et.al in 1989 and 1982 conducted study on young and elderly men and found that this reduction in muscle cross-sectioned area is accompanied by increase in non contractive structures such as fat and connective tissue. Thus, the girth or volume of the muscle band on anthropometric measurements may not show the actual reduction in excitable muscle mass. The total number of muscle fibers is significantly reduced with age beginning at about 25 years and progressing at an accelerated rate thereafter.

Grimby et al (1984), Lexell et al (1988) and Porter et al (1995) have concluded that type II fibers size of vastus lateralis, tibialis anterior and biceps brachii decreases with increasing age, whereas type I fiber size does not change with age. The most basic age related change in muscle morphology at the level of the Motor Unit (MU) is a decrease in the number of total Motor Units. Tomlinson et al (1977) in their study found that loss in MU number is approximately 1% of the total number per annum, beginning in the third decade of life and increasing rapidly in rate beyond the age of 60. Age-related decreases in strength have been well documented. A variety of limb muscles have been tested during isometric strength tasks in young, middle-aged, and older men and women. In general, results of several studies demonstrate that reductions in isometric and dynamic voluntary strength become substantial by the seventh decade of life, and may accelerate thereafter. Healthy men and women in their seventh and eighth decades of life demonstrates average reductions of 20-40% in maximal isometric strength in various muscles, when compared to young adults (McDonagh et al, 1984, Young et al, 1984, Davies et al, 1986, Kallman et al, 1990). These age-related reductions are relatively similar for both sexes and for proximal and distal muscles of various sizes, in both upper and lower limbs. Muscular strength is reported to be highest between the ages of 20 and 30 years. Though, there is progressive decline in maximum strength and which entirely leads to functional loss in activities of daily living.

Research reports indicate that as brain ages or as people get older, there occurs a decrease in brain weight and brain volume, widening of the grooves on the surface of the brain and enlargement of the ventricular system. The decrease in brain weight and brain volume is probably due to the loss of neurons and extra cellular fluid. Man may have a 20% reduction in brain weight between the ages of forty -five and eighty -five and lose thirty to fifty thousand neurons a day from the brain and nervous system as they age. Enlargement of the ventricular system may be probably due to loss of cells surrounding the ventricles. In the first studies of the effects of age on the human Cortex, Brody (1955, 1970) concluded that as many as 50% of neurons are lost with age. Other investigators concurred with this conclusion and it was not until the 1980s that Haug and Terry and their colleagues produced contrary evidence. Haug and his colleagues (Haug, 1984, 1985; Haug et al., 1984) showed that many of the early reports of loss of cortical neurons with age could be attributed to the fact that upon fixation the brains of younger individuals shrink more than those of older ones, which have more myelin. Consequently, when sections of cortical tissue are examined, the young brains show higher neuronal packing densities than those of older individuals. After making corrections for this differential shrinkage, Haug and his colleagues concluded there is no significant loss of neurons from the human cerebral cortex with age. Terry et al (1987) reached a similar conclusion and suggested that much of the neuronal loss recorded in earlier studies could be attributed to brains of some individuals with undiagnosed Alzheimer’s disease being included among the older brains that were being evaluated and considered to be normal. In Alzheimer’s disease there is a significant neuronal loss from cerebral cortex. According to Peter (2002) there is no evidence for a significant loss of cortical neurons during normal aging on the cerebral hemispheres, however there is widespread damage to the myelin sheaths that ensheath their axons, as evidenced by structurally altered myelin sheaths observed in electron microscopic preparations. Although there is no extensive loss of cortical neurons in normal aging, neurons do lose dendritic branches and spines, and there are alterations in the levels of some neurotransmitters and their receptors.

Aging is a process that is often accompanied by physiological changes. These physiological changes include slowing in muscle contractility, alteration in muscle metabolism and neuromuscular junction, and reduction in nerve conduction velocity (NCV). Age has been widely accepted to have an influence on nerve velocity. It is well established that there is a decline in muscular performance with advancing age. Common observations of muscle wasting in the elderly, particularly of proximal limb muscles as well as the small muscles of the hand are reported with aging. Undoubtedly many extraneous factors may contribute to neuromuscular disease in the elderly, of which the most important is probably malnutrition, disuse, circulatory impairment, etc.

Nerve conduction studies (NCS) are the most sensitive and reproducible measure of peripheral nerve functions. Nerve conduction studies (NCS) are performed to diagnose the disorders of the peripheral nervous system. These enable the clinicians to differentiate the two major groups of peripheral diseases: demyelination and axonal degeneration. These also help in localizing the site of the lesions. NCS consist primarily of the assessment of three types of nerves: motor, sensory and mixed. Motor NCS include the assessment of the compound muscle action potential (CMAP), whereas sensory NCS include the assessment of the sensory nerve action potentials (SNAP) of the accessible peripheral nerves in the upper and lower limbs. The median, ulnar, radial, common peroneal, tibial and the sural nerves are the commonly examined nerves. The commonly measured parameters of the CMAP include latency, amplitude, duration, conduction velocity and late response, e.g., F-waves. Similarly, for SNAP, latency, amplitude and conduction velocity are routinely measured. Nerve conduction parameters may be affected by anthropometric factors like age, sex, height, weight and BMI. As it has been reported that significant slowing of conduction velocities and sensory latencies occur with increasing age and more height. It was claimed further that the conduction velocity is 6 m/sec faster in females. Flack et al (1994) reported in their study that the conduction velocity in a newborn is approximately 50% of adult values and progressively increase, reaching the adult value at the age of three. Later in adulthood, the nerve velocity decreases with age and this is more pronounced in the lower than in the upper limbs. Rivner et al (2001) studied that the correlation of NCV with height was stronger than with age. Regression equations using both factors account for 12-27% of the variance. Responses were seen in the majority of patients aged 70 years and older, but the percentage of normals who had no response increased with advancing age. Age was strongly inversely correlated with the amplitudes of both sensory and motor responses, accounting for 7-16% of the variance. Regression equations using both height and age improved this correlation and accounted for 7-22% of the variance.

Over relatively wide temperature ranges, motor and sensory nerve conduction velocities have a positive linear relationship with body temperature. With cooling, motor and sensory amplitudes increase and conduction values decrease. Cooling is thought to affect muscle and nerve membrane function, particularly the sodium ion channel. A direct relationship was observed between the distal sensory amplitude of sural sensory nerve action potential and the temperature of the leg. Henriksen (1956) studied the temperature effects from 12° to 40°C on the motor conduction of human nerves. He found that between 29° and 38°C the motor conduction velocity decreased 2.4 m/sec for each 1°C decrease in temperature. Similar decreases in neural conduction as a function of a 1°C decrease in limb temperature were reported by Buchthal and Rosenfalck (1971) (2.0 m/sec), McLeod (2.6 m/sec), deJesus et al (2.1 m/sec), Ludin and Beyeler (1977) (1.51 m/sec), and Bolton et al (1981) (2.1 m/sec). Ludin and Beyeler (1977) have repotted that between 22° and 26°C the amplitude of SNAPs decreased with lowering temperatures of the limb. Oh (1982) and Ludin and Beyeler (1977) attributed an increase in SNAP amplitude with a concomitant increase in limb temperature to a smaller temporal dispersion of the SNAPs for different fibers and to a sequential shortening of the SNAP spike. As temporal dispersion diminishes with an increase in limb temperature, the SNAP amplitude increases. Bolton et al (1981) however, found that between limb temperatures of 21° to 31°C, the amplitude of the SNAP showed a progressive linear increase with decreasing temperature. This increase in SNAP amplitude with decreasing temperatures may be explained by a decrease in temporal dispersion rather than a real increase in height (amplitude) of the SNAP.

The negative relationship between height and sensory amplitudes was a consistent finding in sensory nerves tested in most of the studies. While controlling for age and surface temperature, height explained much of the sensory amplitude variation (partial R2 in 0.20 to 0.25 ranges). Our results duplicated those of others who have found a strong negative correlation between height and either sural or peroneal conduction velocity. Soudmand et al (1982) studied the effect of height on nerve conduction velocity (NCV) on 41 normal subjects and found that peroneal and sural NCV correlated inversely with height and with estimated axonal length, whereas median motor and sensory NCV failed to show any significant relationship to height. Thakur (2011) in there study on 34 healthy subjects also supported result of various studies that height has a negative correlation with the sensory nerve action potential amplitudes.

The findings of various research studies show that there is no significant difference between race and nerve conduction. In a comparative study done by Ralph et al on 50 Blacks and 50 Whites it was concluded that there was no significant difference between blacks and whites in normal nerve conduction study findings in healthy adults.

The results of various literatures revealed that there is no significant difference between gender and median or ulnar nerve conduction measures in healthy subjects. The results was supported by study done by Stetson (1982) on 105 asymptomatic healthy adults in which it was found that there is no association between sex and median or ulnar nerve conduction measures. For the sural nerve, using a model which also included age, midcalf temperature, and height, women were found to have significantly smaller amplitude and slower conduction velocity then men. The most plausible hypothesis is that both sex and sural nerve conduction and amplitude are correlated with an anatomical or physiological factor which we did not measure. Our results were also supported by study done by Greathouse (1989) on 22 healthy subjects which also explains that there is no significance difference between gender and nerve conduction measures. But Thakur (2010, 2011) in a gender based study on 34 healthy subjects concluded that gender has definite effects on NCS variables. Males had higher CMAP amplitude, longer latencies and duration. Sensory nerve action potential latencies and duration were longer in males whereas amplitude was higher in females. Without adjustment for these factors, the sensitivity and specificity of NCS will decrease when using the same reference data in patients with different gender.