Computer-assisted FES during leg cycling has been shown to be an important and practical means of exercising a relatively large muscle mass in persons with SCI (Hooker et al 1992). These devices also permit the activation of the skeletal muscle pump during leg cycling. For these reasons, FES training has been advocated widely as an effective treatment strategy for SCI. It is important to note, that the physiological responses to FES training appear to be distinct from arm ergometry training. For instance, arm exercise has been shown to lead to faster VO₂ kinetics (at a constant workload), greater changes in HR, and lower post-exercise blood lactates than FES leg cycling (Barstow et al 2000).

We identified 12 pre-post (Griffin et al 2009, Janssen and Pringle 2008, Zbogar et al 2008, Crameri et al 2004, Hopman et al 2002, Gerrits et al 2001, Mohr et al 1997, Hjeltnes et al 1997, Barstow et al 1996, Hooker et al 1992, , Faghri et al 1992, Ragnarsson et al 1988)studies (n = 132) that examined the effectiveness of FES leg cycle ergometry on indices of cardiovascular fitness and/or health in SCI. We also identified 6 pre-post (Thijssen et al 2006, Thijssen et al 2005, Gurney et al 1998, Mutton et al 1997, Krauss et al 1993, Pollack et al 1989)investigations (n = 55) that examined hybrid FES (combined leg and arm ergometry) on cardiovascular fitness in SCI. There were a further 7 pre-post (Berry et al 2008, Stoner et al 2007, Sabatier et al 2006, de Groot et al 2005, Wheeler et al 2002, Jacobs et al 1997, Solomonow et al 1997)investigations (n = 118) that examined the effects of other electrically assisted training programs on cardiovascular fitness and/or health.

FES Leg Cycle Ergometry

Table 5: Effects of functional electrical stimulation on cardiovascular fitness. 

Hybrid FES (Combined Leg and Arm Ergometry)

Table 6: Effects of hybrid FES training on cardiovascular fitness and health.

Other Electrically-Assisted Training Programs

Table 7: Effects of other electrically assisted training programs on cardiovascular fitness and health.

Discussion

There is a growing body of literature indicating that FES exercise training is an effective way of improving cardiovascular health, peak power output, and exercise tolerance/capacity in persons with SCI (Table 5). These studies generally employ a cycling motion, although rowing and bipedal ambulation have also been evaluated. It appears that moderate-to-vigorous intensity FES training (relative to baseline capacity) may be effective in enhancing cardiovascular fitness in persons with SCI. The majority of the investigations are pre-post designs (level 4) with investigators reporting marked changes in VO2max or VO2peak after FES training. Similar to aerobic training, 20%–40% changes in aerobic capacity are often observed after FES training. However, improvements in excess of 70% are not uncommon.(Faghri et al 1992)

Investigations with FES training have also shown an improvement in musculoskeletal fitness. Similar to arm exercise training, limited investigations have shown an improvement in cardiac function after FES training. A recent investigation has also revealed that the degree of muscular adaptation that can be achieved via FES exercise is dependent upon the load that is applied to the paralyzed muscle (Crameri et al 2004).

Researchers have also shown that hybrid exercise training (FES leg cycling combined with arm ergometry) may elicit greater changes in peak work rates and VO2peak/VO2max than FES leg- cycling exercise alone ( Mutton et al 1997, Krauss et al 1993). Moreover, it appears that the physiological adaptations to combined FES leg cycling and arm ergometry training are partially maintained after eight weeks of detraining (Gurney et al 1998). Other interventions (Table 7) that make use of hybrid FES training have also been shown to improve the exercise capacity and cardiovascular health of persons with SCI. It would appear that the potential adaptations with hybrid exercise may be greater than FES alone; however, further research is required to test this hypothesis.

A series of intrinsic muscle adaptations can also occur after FES training that enhance the ability for oxidative metabolism at the cellular level, which in turn facilitate improved endurance, exercise tolerance and functional capacity. Key intrinsic muscle adaptations that have been observed include an increase in the proportion of type 1 fibres, an enhancement in cross-sectional fibre area, an increase in capillary-to-fibre ratio, a shift towards more fatigue resistant contractile proteins, and an increase in citrate synthase activity. Given the importance of musculoskeletal fitness for health and functional status ( Warburton et al 2006c, Warburton et al 2001b, 2001a), further research is clearly warranted with persons with SCI. Accordingly, randomized, controlled exercise interventions (both arm and/or FES training) that evaluate concurrent changes in musculoskeletal fitness and health status are particularly needed.

Conclusion

• There is level 4 evidence from multiple pre-post studies that FES training performed for a minimum of three days per week for two months may be effective for improving musculoskeletal fitness, the oxidative potential of muscle, exercise tolerance, and cardiovascular fitness.
• There is level 4 evidence from multiple pre-post studies that FES training may be effective in improving exercise cardiac function in persons with SCI.
• There is level 5 evidence that arm-cranking exercise assisted by FES increases peak power output, and may increase oxygen uptake.

• Interventions that involve FES training a minimum of 3 days per week for 2 months may improve muscular endurance, oxidative metabolism, exercise tolerance, and cardiovascular fitness.