Thoracic position effect on shoulder range of motion, strength, and three-dimensional scapular kinematics.

OBJECTIVES: To determine the effect of thoracic posture on scapular movement patterns, active range of motion (ROM) in scapular plane abduction, and isometric scapular plane abduction muscle force. STUDY DESIGN AND METHOD: Repeated measures design. There were 34 healthy subjects (mean age, 30.2 yrs). Each subject was positioned and stabilized while sitting in both erect and slouched trunk postures. In each sitting posture a three-dimensional electromechanical digitizer was used to measure thoracic flexion and scapular position and orientation in three planes. Measurements were taken with the arm (1) at the side, (2) abducted to horizontal in the scapular plane, and (3) at maximum scapular plane abduction. In each posture, isometric abduction muscle force was measured with the arm at the side and abducted to horizontal in the scapular plane. RESULTS: In the slouched posture, the scapula was significantly more elevated in the interval between 0 to 90 degrees abduction. In the interval between 90 degrees and maximum abduction, the slouched posture resulted in significantly less scapular posterior tilting. There was significantly less active shoulder abduction ROM in the slouched posture (mean difference = 23.6 degrees +/- 10.7 degrees). Muscle force was not different between slouched and erect postures with the arm at the side, but with the arm horizontal muscle force was decreased 16.2% in the slouched position. CONCLUSION: Thoracic spine position significantly affects scapular kinematics during scapular plane abduction, and the slouched posture is associated with decreased muscle force.     

Strategies that improve human skeletal muscle performance during repetitive, non-isometric contractions

Previous studies have suggested that during sustained maximal voluntary and evoked contractions, decreasing activation rates may minimize fatigue. The idea of gradually decreasing stimulation frequency to preserve force during fatiguing isometric contractions has, however, recently been challenged. The primary purpose of this study was to test the effectiveness of decreasing or increasing electrical stimulation rates during evoked, repetitive, submaximal, non-isometric contractions of healthy human quadriceps femoris muscles. The ability of the muscles to produce a 50° knee excursion repetitively was evaluated using low-frequency trains, high-frequency trains, and a combination of these trains. Results showed that stimulating the muscles with high-frequency trains followed by low-frequency trains produced the worst performance and starting with low-frequency trains followed by high-frequency trains produced the best performance. Present results cast doubt on the applicability of decreasing stimulation rates during non-isometric contractions and suggest that a combination of trains that begin at a low frequency and then switch to a higher-frequency may improve performance during functional electrical stimulation.     

Strategies that improve paralyzed human quadriceps femoris muscle performance during repetitive, nonisometric contractions

OBJECTIVE: To determine the effect of combining different stimulation frequencies on the ability of paralyzed human quadriceps muscle to produce a 50 degrees knee excursion repetitively when starting at 90 degrees of flexion. DESIGN: Repeated-measures design. SETTING: Clinical research laboratory. PARTICIPANTS: Complete data were collected from 9 subjects aged 11 to 25 years (mean +/- standard deviation, 17.1+/-4.5y) with spinal cord injury (SCI). INTERVENTION: Three protocols were each tested during separate sessions: 20-Hz trains of pulses followed by 66-Hz trains (C20+66), 33-Hz trains followed by 66-Hz trains (C33+66), and 66-Hz trains alone (C66). For each frequency, stimulation was repeated until the knee failed to produce a 50 degrees excursion. This approach allowed us to evaluate the response to stimulation with 20-, 33-, and 66-Hz and combinations of 20- and 66-Hz and 33- and 66-Hz trains. MAIN OUTCOME MEASURE: Number of successful contractions. RESULTS: The C20 and C33 did not differ (mean, 41.0+/-12.6 excursions and 42.0+/-12.3 excursions, respectively), and each produced more excursions than the C66 protocol. The C20+66 and C33+66 protocols produced 51.4+/-15.0 and 44.9+/-13.6 excursions, respectively, and the C20+66 was the best protocol overall (all P相似文献   

A novel stimulation pattern improves performance during repetitive dynamic contractions

The purpose of this study was to determine the effect of three different stimulation patterns on repetitive knee movements. Each subject's quadriceps femoris was stimulated with: (1) a constant-frequency train (CFT) with an interpulse interval (IPI) of 50 ms; (2) a variable-frequency train (VFT)-similar to the CFT, except with an initial doublet with an IPI of 5 ms; and (3) a doublet-frequency train (DFT) with multiple doublets (doublet IPI 5 ms) separated by 50 ms, while the muscle was resisted by a load equal to 10% of the muscle's maximum voluntary isometric contraction. The muscle was stimulated while the knee moved through a 50 degrees arc of motion (90 degrees to 40 degrees of flexion). Testing was stopped when the subject failed to reach the target three consecutive times. Results showed that DFTs reached the target (mean +/- SD) 36.4 +/- 14.4 times, followed by VFTs (25.4 +/- 17.9) and CFTs (17.4 +/- 11.9). The DFT was the best pattern for producing shortening contractions. The results suggest that DFTs may have significant benefits during clinical functional electrical stimulation.