In general, investigators have noted significant increases of lower limb strength following locomotor training – despite variations between training protocols and specific methods employed. Outcome measures have included manual muscle testing of individual lower limb muscles in incomplete SCI or summated scores of several muscles (Hornby et al., 2005; Wirz et al., 2005; Field-Fote, 2001; Wernig et al., 1998; Wernig et al., 1995; Granat et al., 1993). Most recent studies have adhered to AIS international guidelines for manual muscle testing (Hornby et al., 2005a; Hornby et al., 2005b; Wirz et al., 2005; Field-Fote, 2001; Field-Fote & Roach, 2011; Tester et al., 2011; Benito-Penalva et al., 2010). Others have employed muscle torque measurements by employing strain gauge transducers (Petrofsky, 2001; Granat et al., 1993), a dynamometer, or twitch interpolation technique (Jayaraman et al., 2008).
All investigators have reported increases in lower limb muscle strength in individuals with chronic SCI. One study (Benito-Penalva et al., 2010) also found similar increases in a group with subacute SCI (< 3 months post-injury). However, several investigators have noted that enhanced walking capability was not necessarily associated with parallel increases in strength (Wirz et al. 2005; Field-Fote, 2001; Field-Fote & Roach, 2011; Wernig et al., 1998; Wernig et al., 1995). Furthermore, the clinical relevance of the small strength gains following locomotor training is questionable when considering the duration and complexity of the intervention (Field-Fote, 2001). However, there is weak evidence (from 1 study, n = 3) that significant improvements in muscle strength may be realized when locomotor training is combined with conventional therapy (Hornby et al., 2005b). In a more recent study that examined the effects of a 12-week resistance and plyometric training program, improvements in knee extensor and ankle plantarflexor torque production were accompanied by >30% improvement in gait speed (Gregory et al., 2007).
Detecting group differences in strength gains during the acute phase may be more challenging given the natural recovery. Wernig et al. (1995) found no differences between those provided locomotor training versus those treated conventionally in muscle strength gains. However, specific subject characteristics were inadequately described other than stating that body-weight supported treadmill training was initiated within a few weeks (i.e., 2-20 weeks, median 7 weeks) following injury. There was also a lack of standardized assessment, further confounding the findings.
There is level 1b evidence (Field-Fote & Roach 2011) that most forms of locomotor training (i.e., including body weight supported treadmill training with various assists and FES-assisted overland training) increase lower limb muscle strength in chronic SCI as indicated by overall increases in total lower extremity motor scores.
There is level 3 evidence (Wernig et al. 1995) that body weight supported treadmill training is not significantly different than conventional rehabilitation therapy in enhancing lower limb muscle strength in acute SCI, although these studies are confounded by the natural recovery that may take place in the acute period.
There is level 4 evidence (Gregory et al. 2007) that a resistance and plyometrics training program can enable improvements in overground gait speed in chronic incomplete SCI.
Locomotor training programs are beneficial in improving lower limb muscle strength although in acute SCI similar strength increases may be obtained with conventional rehabilitation.
The real benefit of locomotor training on muscle strength may be realized when it is combined with conventional therapy. This should be further explored in acute, incomplete SCI where better functional outcomes may be realized with the combination of therapies.