Rating of Perceived Exertion as an Indicator of Exercise Intensity in Paraplegics

Background: Energy expenditure is of paramount importance in the assessment of usefulness of wheelchair for paraplegics. Despite widespread recognition of problems associated with currently available mobility systems for persons with spinal cord injuries, development of more efficient systems has been slow.  Lack of a suitable and simple technique for the assessment of energy expenditure in paraplegics has perhaps contributed to this slowness.  Objective: To assess the energy expenditure with a simple technique, i.e. rating of perceived exertion during arm crank ergometry and crutch walking in paraplegics. Methods: The experiments can be divided into three phases; firstly, assessment of energy expenditure during seated arm crank ergometry in 10 paraplegics and 20 able-bodied subjects; secondly, upright arm crank ergometry in seven paraplegics and 20 able-bodied subjects.  Arm crank ergometry was carried out with an incremental series protocol at three work rates (16, 28 and 40 watts) and at a cranking rate of 50 rpm.  The third part was to assess the energy expenditure during crutch walking in five paraplegics and in 10 able-bodied subjects whilst walking with axillary crutches and knee-ankle-foot orthoses.  All subjects walked at their preferred speed on a figure of eight track.  We measured the oxygen consumption, using the Douglas bag technique or the face mask method, and evaluated the rating of perceived exertion by the standard 6-20 Borg scale. Results: The non-significant difference of two measured variables (oxygen consumption and rating of perceived exertion) between paraplegic and able-bodied subjects showed the consistency of measured variables for the assessment of energy expenditure during seated arm activities (e.g., wheelchair propulsion) in paraplegics.  However, during upright arm crank ergometry, paraplegics found work at any given rate harder upright than seated.  The results indicated a greater load on the cardiorespiratory system in paraplegics during crutch walking.  The different responses to these types of arm exercises in thoracic paraplegics could be partly or wholly explained by impaired mechanisms of venous return in paraplegics, problems that would be particularly severe in upright posture.  In addition, dividing by speed standardizes, both the energy cost and the physiological cost index; this has not been done for perceived exertion.Conclusion: Though more high lesion patients should obviously be studied, this strongly suggests that perceived exertion is not a suitable indicator for comparison among subjects whose preferred walking speeds are different.  However, for comparison between individuals, crutch walking at a given speed on treadmill could be of value.