LONG-TERM ADAPTATION TO ELECTRICALLY-INDUCED CYCLE TRAINING IN SEVERESPINAL-CORD INJURED INDIVIDUALS

Spinal cord injured (SCI) individuals most often contract their injury at a young age and are deemed to a life of more or less physical inac tivity. In addition to the primary implications of the SCI, severe SCI individuals are stigmatized by conditions related to their physically inactive lifestyle. It is unknown if these inactivity related conditi ons are potentially reversible and the aim of the present study was, t herefore, to examine the effect of exercise on SCI individuals. Ten su ch individuals (six with tetraplegia and four with paraplegia; age 27- 45 years; time since injury 3-23 years) were exercise trained for 1 ye ar using an electrically induced computerized feedback controlled cycl e ergometer. They trained for up to three times a week (mean 2.3 times ), 30 min on each occasion. The gluteal, hamstring and quadriceps musc les were stimulated via electrodes placed on the skin over their motor points. During the first training bouts, a substantial variation in p erformance was seen between the subjects. A majority of them were capa ble of performing 30 min of exercise in the first bout; however, two i ndividuals were only able to perform a few minutes of exercise. After training for 1 year all of the subjects were able to perform 30 min of continuous training and the work output had increased from 4 +/- 1 (m ean +/- SE) to 17 +/- 2 Kilo Joules per training bout (P<0.05). The ma ximal oxygen uptake during electrically induced exercise increased fro m 1.20 +/- 0.08 litres per minute measured after a few weeks habituati on to the exercise to 1.43 +/- 0.09 litres per minute after training f or 1 year (P<0.05). Magnetic resonance cross sectional images of the t high were performed to estimate muscle mass and an increase of 12% (me an, P<0.05) was seen in response to 1 year of training. In biopsies ta ken before exercise various degrees of atrophy were observed in the in dividual muscle fibres, a phenomenon that was partially normalized in all subjects after training. The fibre type distribution in skeletal m uscles is known to shift towards type IIB fibres (fast twitch, fast fa tiguable, glycolytic fibres) within the first 2 years after the spinal cord injury. The muscle in the present investigation contained of 63% myosin heavy chain (MHC) isoform IIB, 33% MHC isoform IIA (fast twitc h, fatigue resistant) and less than 5% MHC isoform I (slow twitch) bef ore training. A shift towards more fatigue resistant contractile prote ins was found after 1 year of training. The percentage of MHC isoform IIA increased to 61% of all contractile protein and a corresponding de crease to 32% was seen in the fast fatiguable MHC isoform IIB, whereas MHC isoform I only comprised 7% of the total amount of MHC. This shif t was accompanied by a doubling of the enzymatic activity of citrate s ynthase, as an indicator of mitochondrial oxidative capacity. It is co ncluded that inactivity-associated changes in exercise performance cap acity and skeletal muscle occurring in SCI individuals after injury ar e reversible, even up to over 20 years after the injury. It follows th at electrically induced exercise training of the paralysed limbs is an effective rehabilitation tool that should be offered to SCI individua ls in the future.