As with people without SCI, there is strong evidence in support for the use of exercise training for improving cardiovascular health among people with SCI (see Cardiovascular Heath and Exercise chapter). This is important because there is a high incidence of physical inactivity in people with SCI and as such, they are at increased risk of secondary conditions such as cardiovascular disease, diabetes, osteoporosis, and obesity. There is clear evidence that the cardiovascular and skeletal muscle systems adapt positively to exercise training in with or without SCI. However, the lungs and airways do not change appreciably in response to exercise training. It is likely that exercise is not sufficiently stressful to warrant an adaptive response. This may be even more so when considering the small muscle mass used in wheelchair propulsion or arm cranking exercise. On the other hand, respiratory muscles are both metabolically and structurally plastic and they respond to exercise training. This statement is based largely on direct evidence from animal models and indirect evidence from able-bodied humans.
Exercise training may influence the control of breathing and respiratory sensations (i.e., dyspnea). It is generally accepted that exercise training results in a lower VE at any given absolute oxygen consumption or power output. This is likely due to a reduction in one or more of the mechanisms (neural and/or humoral) purported to cause the hyperpnea (increased respiratory rate) associated with exercise. As such, the positive effects of exercise training in SCI may reside in an increase in respiratory muscle strength and endurance as well as a reduced ventilatory demand during exercise. A lower ventilation and/or sensation of dyspnea during exercise would lower the work of breathing and prevent early termination of exercise, respectively.
Evidence for exercise training for the respiratory management in patients with SCI includes 6 RCTs, 6 prospective controlled trials and cohort studies, and 19 lower-level studies (mainly pre–post studies). Studies describing the acute responses to exercise in people with SCI were not included nor were studies that investigated competitive athletes with SCI. Included studies were difficult to interpret because of relatively small sample sizes, differences in exercise modality (wheelchair, arm crank exercise, body weight supported treadmill training, exoskeleton-assisted walking, functional electrical stimulation (FES) rowing, exergaming, pulmonary rehabilitation (strength training combined with respiratory training), passive leg cycling, or overground locomotion training) as well as inconsistent frequency, intensity and duration of exercise training. Nine studies included a control group (Silva et al. 1998; Carvalho et al. 2006; Lee et al. 2012; Moreno et al. 2013; Tiftik et al. 2015; Chen et al. 2016; Vivodtzed et al. 2020a; Vivodtzed et al. 2020b; Xiang et al. 2021), and the control groups in seven of the studies included participants comparable to those in the treatment group. This is in contrast to the control group used in Silva et al. 1998 study which consisted of non-SCI participants only; though healthy controls may be used for the normative values, they cannot be considered a true control group for people with SCI.
There is insufficient evidence to strongly support exercise training as a means to improve pulmonary function or ventilatory responses to exercise in people with SCI. However, some evidence (Le Foll-de-Moro et al. 2005; Qiu et al. 2016; Panza et al. 2019; Chen et al. 2016) indicated that following exercise training, VO2peak, aerobic efficiency (oxygen uptake efficiency slope [OUES]), FEV1, FVC, maximal ventilation volume, FEV1/FVC, peak VE, VT and ventilatory reserve improve. Two RCTs found significantly increased respiratory capacity testing exoskeleton (Xiang et al. 2021) walking or FES rowing (Vivodtzed et al. 2020b) with NIV when compared to sham training. Nevertheless, the training intensity needs to be relatively high (70-80% of maximum heart rate at a minimum of 3x/week for 6 weeks) as lower intensities did not show similar efficacy (Hooker & Wells 1989). Other studies showed no change in pulmonary function or ventilation during exercise (Valent et al. 2008; Jacobs 2009). Although 6 months of body-weight supported treadmill training in conjunction with neuromuscular electrical stimulation (NMES) was shown to be effective for improving peak measures of respiration, the intensity at which participants worked to achieve these outcomes is unclear, as each performed according to their individual capacity (Carvalho et al. 2006).
There is level 1 evidence (from one RCT: Xiang et al. 2021) that exoskeleton-assisted walking training for 4 weeks produces improvements at short-term in predicted FVC%, FEV1, FEF75, PEF, and MVV; and higher improvements in FVC, predicted FVC% and FEV1 compared with conventional strength, aerobic, and balance training in patients with SCI.
There is level 2 evidence (from one RCT: Vivodtzed et al. 2020b) that whole-body hybrid FES-rowing training for 3 months with NIV provided better improvements in aerobic efficiency (OUES) (with an overall reduction in peak breathing frequency) and VO2peak compared with the same training with sham NIV in patients with SCI.
There is level 4 evidence (from one pre-post study: Brizuela et al. 2020) that improvements in pulmonary parameters are higher in participants with lower cervical SCI than in participants with high cervical SCI after a stationary armcrank exercise for 8 weeks.
There is level 2 evidence (from two prospective controlled trials: Carvalho et al. 2006; Tiftik et al. 2015; and from one RCT: Chen et al. 2016) and level 4 evidence (from six pre-post studies: Silva et al. 1998; Sutbeyaz et al. 2005; Le Foll-de-Moro et al. 2005; Fukuoka et al. 2006; Terson de Paleville et al. 2013; Qiu et al. 2016) to support exercise training as an intervention that might improve resting and exercising respiratory function, and VO2peak, and OUES in people with SCI.
There is level 4 evidence (from four pre – post studies: Panza et al. 2019; Panza & Guccione 2020; Panza et al. 2017; Gollie et al. 2017) that overground locomotor training (OLT) protocol provides some improvement in VE, the phasic response to exercise (became faster), and walking endurance; and reductions in VE variability, VT variability, estimated work of breathing, VCO2, PETCO2, and in RPE in patients with SCI.
There is level 4 evidence (from one pre-post study: Janssen & Pringle 2008) that computer controlled electrical stimulation (ES) induced leg cycle ergometry (ES-LCE) increases the peak values of VO2, CO2, and pulmonary ventilation.