An alternative test of electromyographic normalization in patients

Abstract

The value of electromyography (EMG) in the interpretation of normal and pathological movement depends on recording, processing, and normalization procedures. Traditionally, maximum voluntary isometric contraction (MVIC) of individual muscles is commonly used for EMG normalization. However, this is a time- and energy-consuming procedure, especially in patients. The aim of the present study was to compare an alternative method of recording the MVIC of lower-limb muscles to the traditional method in healthy, young subjects as well as individuals with a stroke. The alternative method consisted of recording the maximum effort of several thigh and leg muscles simultaneously using two tasks on a dynamometer. Five healthy subjects and five individuals who had a stroke performed both MVIC tasks. The healthy group repeated the test 3 h later on the same day. In general, the method of computing maximum EMG from the alternative MVIC test yielded values that were equal or greater than those from the traditional test in both groups. In the healthy group, muscles showed similar EMGs in the two sessions, indicating that the test was reliable. These results suggest that the less time-consuming alternative method of computing maximum EMG values used here provides a reasonable alternative when time and fatigue become issues, especially when testing patient populations.

Normalization of EMG Signals: To Normalize or Not to Normalize and What to Normalize to?

“…• knee extension, knee flexed 90°, hip flexed 90° (sitting) [38,43] • knee extension, knee flexed 60°, hip flexed 90° (sitting) [44,45] • knee extension, knee flexed 45° (sitting) [37] vastus medialis • knee extension, knee flexed 60° (sitting) [44,45] • knee extension, knee flexed 90°, hip flexed 90° (sitting) [43] rectus femoris • knee extension, knee flexed 90°, hip flexed 80° to 90° (sitting) [35,36,38,43] • knee extension, knee flexed 60°, hip flexed 90° (sitting) [44][45][46] lateral hamstring (biceps femoris) long head…”

“…• knee flexion, knee flexed 90°, hip flexed 90° (sitting) [38] • knee flexion, knee flexed 60° (sitting) [44,46] • knee flexion, knee flexed 60° (prone) [45] • knee flexion, knee flexed 90°, hands clasped behind head (prone) [37] gastrocnemius lateralis…”

“…• ankle plantar flexion, ankle -15°, knee flexed 30° [44] • ankle plantar flexion, mid ankle position (standing unilateral -body weight) [47] • ankle plantar flexion, ankle, knee and hip in neutral position (prone) [45] gastrocnemius medialis…”

“…• ankle plantar flexion, ankle, knee and hip in neutral position (prone) [38,45] • ankle plantar flexion, ankle -15°, knee flexed 30° [44] • ankle plantar flexion, mid ankle position (standing unilateral -body weight) [47] • ankle plantar flexion (supine) [33] soleus • ankle plantar flexion, mid ankle position (prone) [38] • ankle plantar flexion, ankle in neutral position; knee and hip flexed 90° (quadruped position) [45,46] tibialis anterior • ankle dorsi flexion, ankle, knee and hip in neutral position (supine) [45] • ankle dorsi flexion, ankle in neutral position; knee and hip flexed 90° (quadruped position) [46] Although the repeatability of the EMG recorded during MVICs within individuals on the same day has been questioned [34], the majority of studies indicate that the reliability of MVICs within individuals on the same day is high [42,48,49]. High repeatability requires proper guidance of the subjects to perform the tests identically with each repetition, familiarity of the subjects with the production of maximum effort and the avoidance of fatigue.…”

“…Since the use of MVICs is the most valid method to normalize EMG data allowing comparison of activity levels between muscles in different individuals, it should be the normalization method of choice when evaluating muscle function in clinical populations provided symptomatic individuals can produce MVICs. Indeed recent studies have shown that individuals from some clinical populations (moderate knee osteoarthritis [58], following knee surgery [103], back pain [104,105], cerebral palsy [106], stroke [45,107]), are able to produce maximum activation levels using the same MVIC tests as healthy individuals [8]. If symptomatic individuals are unable to elicit maximal contractions, e.g.…”