Evaluation of Aerobic Capacity and Strength
Methods for the evaluation of strength in people with ALS include a clinical neurological exam, manual muscle testing (MMT), and rating scales. These methods are subjective and lack sensitivity to detect small changes (Agre, Magness, Hull, Wright, Baxter, Patterson, & Stradel, 1987; Andres, Hedlund, Finison, Conlon, Felmus, & Munsat, 1986; Goonetilleke, Modares-Sadeghi, & Guiloff, 1994; Wiles & Karni, 1983). Strength depends on many factors, including the type of contraction, speed of contraction, length-tension relationship, neuronal discharge, cross-sectional area of muscle, and motivation (Andres et al., 1986).
Tourtellotte et al. (cited in Andres et al., 1986) developed a quantitative measurement system to evaluate multiple sclerosis that uses measured date rather than grading scales. Andres et al. (1986) developed a similar set of standardized tests for people with ALS. The test, the Tufts Quantitative Neuromuscular Exam (TQNE), possesses the following features:
- quantitative scores generate interval data;
- low test-retest variation;
- records both mild and severe impairment accurately;
- measures both upper and lower motor neuron functions;
- assesses different levels of the neuraxis;
- is time-efficient;
- is inexpensive;
- is sensitive to small changes;
- is easy to learn for both the examiner and patient;
- can be computer-stored and analyzed; and
- is suitable for multi-institutional studies (Andres et al., 1986).
The four sections of the test are pulmonary function, oropharyngeal, timed motor activities, and maximal isometric strength. Pulmonary function tests measure forced vital capacity and maximum voluntary ventilation; oropharyngeal measures diadochokinetic syllable production; timed motor activities measure the dexterity of each hand and speed of walking 15 feet; and maximal isometric strength tests isometric force of nine muscle groups bilaterally and hand grip strength.
The TQNE reduces the error of the isometric strength testing due to positioning, patient instruction, verbal encouragement, muscle contraction/relaxation time, and stabilization (Andres et al., 1986). Directing quantitative measurement of spasticity is still a problem. The timed walking and timed hand activities may indirectly give evidence of the degree of spasticity (Andres et al., 1986).
In a study by Wiles and Karni (1983), the measurement of the strength of a maximum voluntary contraction is the simplest and most direct means of assessing the amount of active muscle in a particular group. In a disease, this contraction is reduced due to the amount of contractile material or activation impairment, or both. They found that in muscle disease, the maximum voluntary contraction reflects the amount of functioning contractile muscle, assuming normal excitation processes. With a disease of the central or peripheral nervous system, strength changes reflect altered excitation processes, and muscle mass is secondary. In this study, they claim that these uncertainties can be overcome by always performing the measurements in the same manner following an established routine, but this is probably not the best method to determine strength in a person with ALS.
Studies by Agre et al. (1987) and Goonetilleke et al. (1994) examined the reliability, accuracy, reproducibility, and variability of hand-held dynamometry in the assessment of both upper- and lower-extremity strength. The study by Goonetilleke et al. (1994) was specific to motor neuron disease. Variability is high when using dynamometry to measure lower-extremity strength; dynamometry is better used for upper-extremity strength measurement (Agre et al., 1987). Goonetilleke et al. (1994) determined that there was no difference in variability when reporting the results of three trials on handgrip strength. Variability did not change with reporting the highest value, the mean, or the median. The mean is prone to the effects of abnormally high or low readings in one assessment due to fatigue, but there was still no difference in variability. To assess handgrip strength in people with ALS, the mean should be reported, due to fatigue causing possible differences.
Lower free fatty acids (FFA), ketones, and esterified carnitine in the plasma during exercise and 90 minutes post-exercise were observed in the people with ALS. The lower plasma FFA may indicate increased FFA mobilization from adipose tissue. A conclusion drawn from this study is that patients with ALS exhibit specific abnormal physiologic and metabolic responses to exercise (Sanjak et al, 1987). This includes decreased work capacity, increased oxygen cost of submaximal exercise, and abnormalities in plasma and muscle lipid metabolism. It is important to note that these abnormalities did not prevent the patients with ALS from performing prolonged exercise. Specific delineation of all abnormalities in energy production and substrate utilization is an important prerequisite for the clinician and exercise specialist in planning a safe and adequate exercise program (Sanjak et al., 1987).
Wright, Kilmer, McCrory, Aitkens, Holcomb, & Bernauer (1996) studied the effects of a 12-week walking program on people with progressive neuromuscular disease. The purpose of the study was to determine the effects of aerobic training in this population, and whether patients would adhere to a self-monitored, home-based exercise program. This study showed moderate-intensity aerobic walking three to four days per week safely produced improvements in work capacity, aerobic capacity, and cardiovascular variables such as decreased heart rate and blood pressure (Wright et al., 1996). Improvement in physical fitness can potentially reduce the strains of daily living by increasing reserve capacities. This would allow individuals to meet the physiological demands required for activities of daily living (ADL) more effectively (Wright et al., 1996). This program was safe and well adhered-to by participants in this study.
A physiological change in people with ALS is an elevated creatine phosphokinase level (CPK). Creatine phosphokinase is an enzyme that is usually in high concentration in muscle tissue to meet the energy demands of the contracting muscle. It is usually elevated in inflammatory and degenerative muscle disease, but normal in neuropathic diseases (DeLisa & Tipton, 1979). CPK levels are elevated in 50% to 75% of the patients with motor neuron diseases, especially ALS (DeLisa & Tipton, 1979); these levels are usually five to six times above normal, but depend on the activity level of the person. (CPK is an intracellular enzyme. As ALS progresses, cells degenerate and rupture, releasing CPK into the blood stream, thus elevating serum levels.) DeLisa and Tipton (1979) found that bed rest will decrease CPK levels, but that moderate exercise will increase the levels. This is normal, even in a healthy population. What is abnormal is that the CPK levels do not return to a normal level even after 24-hour bed rest. As muscle mass decreases with progression of the disease, CPK values return to normal limits.