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The timing and relative intensity of electromyographic activity of hip abductor and extensor muscles were recorded during free and fast velocity walking and during ascent and descent of stairs. Eleven healthy subjects were tested using fine wire electrodes to record the electromyographic activity. Data were quantified by normalizing all electromyographic activity during gait with electromyographic activity occurring during a sustained maximum isometric effort resisted either manually or with a dynamometer. The results indicated that the hip extensor muscles had different phasic patterns and moments of peak activity. During level walking, the semimembranosus and long head of the biceps femoris muscles displayed the greatest swing phase activity (beginning in mid-swing). The adductor magnus muscle followed with its onset in terminal swing. Both this muscle and the gluteus maximus were the principal hip extensors active during the loading response. For ascending stairs, the lower portion of the gluteus maximus muscle proved to be the main hip extensor during the loading response and mid-stance. The findings also showed that the upper portion of the gluteus maximus muscle functioned more like the gluteus medius muscle than the lower portion of the gluteus maximus muscle during both level and stair walking.

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Shoulder injuries in tennis players are common because of the repetitive, high-magnitude forces generated around the shoulder during the various tennis strokes. An understanding of the complex sequences of muscle activity in this area may help reduce injury, enhance performance, and assist the rapid rehabilitation of the injured athlete. The supraspinatus, infraspinatus, subscapularis, middle deltoid, pectoralis major, latissimus dorsi, biceps brachii, and serratus anterior muscles were studied in six uninjured male Division II collegiate tennis players using dynamic electromyography (EMG) and synchronized high-speed photography. Each subject performed the tennis serve and the forehand and backhand groundstrokes, and each stroke was divided into stages. The tennis serve contains four stages. Three stages characterize the forehand and backhand groundstrokes. Our results indicate that the subscapularis, pectoralis major, and serratus anterior display the greatest activity during the serve and forehand. The middle deltoid, supraspinatus, and infraspinatus are most active in the acceleration and follow-through stages of the backhand. The biceps brachii increases its activity during cocking and follow-through in the serve with a similar pattern noted in the acceleration and follow-through stages of the forehand and backhand. The serratus anterior demonstrates intense activity in the serve and forehand, thus providing a stable platform for the humeral head and assisting in gleno-humeral-scapulothoracic synchrony. The tennis serve and forehand and backhand groundstrokes are accomplished by complex sequences of muscle activity that incorporate contributions from the lower extremities and trunk into smooth, coordinated patterns.(ABSTRACT TRUNCATED AT 250 WORDS)

The relative selectivity of surface electrodes placed over the gastrocnemius and soleus muscles in the standard manner was determined by comparing the electromyogram from these electrodes to the electromyogram from wire electrodes inserted into the soleus, gastrocnemius, and tibialis posterior muscles. Muscle activity was elicited in 11 normal subjects by performing six manual muscle tests. Three of the tests followed the standard technique and three were modifications designed to provide better differentiation of muscle action. All electromyographic data were quantified by computer integration and normalized to cancel out sampling inconsistency. None of the muscle tests totally restricted activity to the designated muscle, but the tests did determine which was the strongest participant. During the standard specific gastrocnemius and soleus muscle tests, the corresponding surface electrode provided a lower electromyogram than did the matching wire electrode; that is, the surface-to-wire-electrode ratio was less than one (gastrocnemius = 0.74, soleus = 0.58). This ratio was greater than one when the electromyogram was being recorded from one muscle while testing another muscle (gastrocnemius = 1.55, soleus = 1.92). The mathematical model relating surface-electrode values to the wire-electrode data from all three muscles identified 60 percent of the surface gastrocnemius electrode electromyogram as arising from that muscle, while only 36 percent of the soleus surface electrode data related to the activity of the soleus: Sg = .19Ws + 60Wg + .13Wt + .08Wo and Ss = .36Ws + .31Wg + .22Wt + .11Wo.