Assessing kinematics and kinetics of functional electrical stimulation rowing
Introduction
Each year, 11,000 people sustain a spinal cord injury (SCI) in the United States, resulting in an estimated 276,000 people living with a chronic SCI in the US (University of Alabama at Birmingham, 2014). SCI is a life-changing event, resulting in multisystem impairment causing physiological, neurological, and psychological changes. Moreover, the SCI population is at the low end of the fitness spectrum, representing a form of “accelerated aging” (Groah et al., 2012). Hence, after an SCI, there is increased risk of cardiovascular morbidity and mortality (DeVivo et al., 1999, Myers et al., 2007), greater rates of obesity (Groah et al., 2011) and diabetes (Qin et al., 2010), and profoundly accelerated osteoporosis due to rapid decrease in bone density to approximately 60% of normal bone mass (Jiang et al., 2006).
Currently, there is no cure for SCI and effective interventions to maintain and improve health and well-being after injury are needed. Regular physical activity has important multi-system health benefits, and more vigorous exercise is associated with greater benefits (Nelson et al., 2007). SCI does not alter this effect, and in fact may make exercise of critical importance to health (Groah et al., 2012, Hooker and Wells, 1989, Nash et al., 2012, West et al., 2014a). However, this population is typically restricted to only upper body exercise, which involves a smaller amount of muscle mass and limits cardiovascular adaptations compared to lower extremity or combined activities (Figoni, 1993, Gates et al., 2002, Pitetti et al., 1994, Rimaud et al., 2012, West et al., 2014b). To overcome both of these limitations, functional electrical stimulation (FES) of the lower body combined with upper body exercise actively engages more muscle mass and demands greater cardiovascular adjustments, and hence can lead to broad health benefits (Petrofsky and Phillips, 1984).
Hybrid FES-rowing allows the SCI population to exercise their upper and lower limbs concurrently (Laskin et al., 1993). In contrast to other forms of exercise (arms only, FES leg cycling, or FES leg cycling with arm exercise), FES-rowing is unique in that it provides the coordinated engagement of both the innervated arms and the non-innervated legs. The integral performance of this whole body exercise increases the active muscle mass engaged, creating a muscle pump complimentary to the upper body, augmenting blood flow to the heart. Thus, hybrid FES-rowing results in significantly greater metabolic responses than arms only exercise or FES-cycling (Hettinga and Andrews, 2007, Hettinga and Andrews, 2008, Taylor et al., 2011, Verellen et al., 2007, Wheeler et al., 2002). Other forms of FES exercise provide only modest axial loading of the legs, such as FES-cycling (Haapala et al., 2008, Szecsi et al., 2014), and result in little benefit to bone health (BeDell et al., 1996, Eser et al., 2003, Frotzler et al., 2008). Isolated isometric muscle stimulation has been shown to have a positive impact on bone health in those with SCI (Shields et al., 2006, Shields and Dudley-Javoroski, 2006), but has little effect on cardio-respiratory health. It has been suggested by one case report that FES-rowing may provide sufficient magnitude and frequency of loading of the legs to result in therapeutic bone benefits (Gibbons et al., 2014).
Hybrid FES-rowing resembles able-bodied rowing, but the specifics of the rowing stroke, the loading produced, and the mechanical efficiency of those with SCI who habitually train with FES-rowing are unknown. Halliday (Halliday et al., 2004) showed in a single case that motion of the arms, ankle, and knee is similar in FES-rowing as compared to able-bodied rowing. However, FES-rowing demonstrates different rowing stroke timing and external forces at both the handle and feet compared to able-bodied rowing. Optimizing the health benefits of this exercise intervention requires better understanding the kinematics and kinetics of FES-rowing in relation to the aerobic work performed. Therefore, we developed an instrumented ergometer to measure kinetics and kinematics of rowing and open circuit spirometry to determine aerobic demand during both FES-rowing and able-bodied rowing. This allowed us to characterize rowing stroke, effective upper and lower body forces across exercise intensities, and mechanical efficiency of rowing. We hypothesize that greater rowing intensity would require greater upper and lower body forces and greater oxygen consumption in both able-bodied and FES-rowers. We additionally hypothesize that the magnitude of increase in upper and lower body forces, and oxygen consumption will be greater in able-bodied compared to FES-rowing as exercise intensity increases.
Section snippets
Participants
Individuals with SCI (n=6) were recruited from current patients in the Spaulding Rehabilitation Hospital SCI exercise program for FES-rowing and were actively rowing on a weekly basis. All the individuals with SCI were adults with spinal cord injury of American Spinal Injury Association A at the neurological level of C5-T12 (Table 1). All subjects were medically stable, able to follow directions, able to reach sufficient leg joint range of motion to row, and able to respond to electrical
Kinematics and kinetics of FES-rowing
FES-rowing and able-bodied rowing showed a similar distribution of drive (quadriceps activation) and recovery (hamstrings activation, example in Fig. 2) phases of the rowing stroke (drive phase: (47±9)% vs. (53±7)% of rowing stroke (p=0.2); recovery phase: (53±9)% vs. (47±7)% of rowing stroke (p=0.2)). However, FES-rowing had a different pattern of lower and upper body coordination in which the arm pull preceded the leg extension during drive phase such that the arms initiated the stroke with
Discussion
We assessed the kinematics and kinetics of FES-rowing and able-bodied rowing in relation to the aerobic work performed. The FES stroke is characterized by a handle pull that precedes leg extension during the drive phase and by the lack of increase in stroke rate across intensities. This reliance upon handle pull results in a lack of increase in feet force across increasing intensities and may relate to lesser overall mechanical efficiency in FES-rowing. Taken together, these data show that the
Conflict of Interest
The authors have no conflicts of interest to declare.
Acknowledgments
This work was funded by a Northeastern University Dean׳s Scholarship (Adina E. Draghici). This study was supported by National Institute of Health (R01 HL117037). We thank all our subjects for their participation.
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