The relationship between perceived exertion and physiologic indicators of stress during graded arm exercise in persons with spinal cord injuries

Muscle activity differs with load compliance during fatiguing contractions with the knee extensor muscles

The purpose of this study was to determine the influence of load compliance on the time to failure and rate of change in electromyographic (EMG) activity when the knee extensor muscles performed fatiguing contractions against submaximal loads. The low-compliance condition required the subject to exert a force against a rigid restraint (force control), whereas the high-compliance condition involved maintaining the knee joint angle while supporting an equivalent inertial load (position control). Both contractions were sustained for as long as possible. Each subject exerted a similar net torque about the knee joint during the force and position tasks; the target force corresponded to a force at the ankle equal to 20% of the maximal voluntary contraction (MVC) force. Thirteen healthy adults (25 +/- 7 year) participated in the study. MVC forces before the force and position tasks were similar (189 +/- 40 N vs. 179 +/- 43 N, P = 0.4), and the target force was 36 +/- 8 N. The time to task failure was longer for the force task (224 +/- 114 s) than for the position task (110 +/- 36 s, P < 0.05), but MVC force declined to a similar level immediately after task failure for the two tasks (-31 +/- 16%). The briefer time to failure for the position task was accompanied by greater rates of increase in agonist EMG amplitude and the pressor response. Coactivation ratios, in contrast, were similar for the two tasks and did not contribute to task differences in time to failure. These findings indicate that it was more difficult to sustain a submaximal contraction with the knee extensor muscles when the task required position control, despite comparable net muscle torques for the low- and high-compliance tasks.

Aerobic exercise during early rehabilitation for cervical spinal cord injury

BACKGROUND AND PURPOSE

People with spinal cord injuries (SCIs), particularly those with injuries causing tetraplegia, are at risk for cardiovascular illnesses. There is a compelling need to address poor cardiovascular health as early as possible after cervical SCI. The purpose of this case report is to illustrate the process of aerobic exercise prescription during inpatient rehabilitation for cervical SCI.

CASE DESCRIPTION

The patient was a 22-year-old man who had sustained a complete C5 SCI during a swimming accident 12 weeks before he participated in an aerobic exercise program. The program was developed to facilitate aerobic capacity while minimizing muscular fatigue. The patient attended 18 sessions over a 2-month period.

OUTCOMES

The patient's exercise tolerance increased in terms of both exercise duration and exercise intensity. Measurements of cardiovascular health, taken before and after training, revealed substantial increases in peak oxygen uptake (20%) and orthostatic tolerance over the course of the program.

DISCUSSION

The patient experienced typical complications associated with acute SCI (eg, orthostatic hypotension, urinary tract infections). He exhibited several signs of improved exercise tolerance and wheelchair mobility during the 2-month program, indicating potential cardiovascular and functional improvements from the exercise training.

Submaximal arm crank ergometry: Effects of crank axis positioning on mechanical efficiency, physiological strain and perceived discomfort

PURPOSE

To evaluate the effect of the spatial orientation of the crank axis on mechanical efficiency, physiological strain and perceived discomfort in submaximal synchronous arm crank ergometry.

METHODS

Twelve able-bodied individuals performed 12 submaximal exercise bouts of 3 minutes (women: 20 W/25 W; men: 25 W/35 W). The crank axis position was defined by elbow and shoulder angle.

RESULTS

The results showed that a crank set-up with an elbow angle of 30 degrees was more efficient than 15 degrees ; oxygen consumption and minute ventilation were significantly lower. No significant effects were seen for shoulder angle. Power output and gender showed obvious effects.

DISCUSSION AND CONCLUSION

The magnitude of this effect and the absence of any significant shoulder angle effects may be due to the relative low exertion levels that were evaluated. An elbow angle of 30 degrees flexion in arm crank exercise is favourable compared to an elbow angle of 15 degrees in able-bodied untrained subjects.