Date Published: October 9, 2018
Publisher: Public Library of Science
Author(s): Gareth D. Jones, Darren C. James, Michael Thacker, David A. Green, Juan J. Loor.
Rising-to-walk is an everyday transitional movement task rarely employed in gait rehabilitation. Sit-to-walk (STW) and sit-to-stand-and-walk (STSW), where a pause separates sit-to-stand and gait-initiation (GI) represent extremes of rising-to-walk behaviour. Delayed GI can indicate pathological impairment but is also observed in healthy individuals. We hypothesise that healthy subjects express consistent biomechanical parameters, among others that differ, during successful rising-to-walk task performance regardless of behaviour. This study therefore sought to identify if any parameters are consistent between STW and STSW in health because they represent normal rise-to-walk performance independent of pause, and also because they represent candidate parameters sensitive enough to monitor change in pathology.
Ten healthy volunteers performed 5 trials of STW and STSW. Event timing, ground-reaction-forces (GRFs), whole-body-centre-of-mass (BCoM) displacement, and centre-of-pressure (CoP) to extrapolated BCoM (xCoM) distance (indicator of positional stability) up to the 3rd step were compared between-tasks with paired t-tests. For consistent parameters; agreement between-tasks was assessed using Bland-Altman analyses and minimal-detectable-change (MDC) calculations.
Mean vertical GRFs, peak forward momentum and fluidity during rising; CoP-xCoM separation at seat-off, upright, GI-onset, and steps1-2; and forward BCoM velocity were all significantly greater in STW. In contrast, peak BCoM vertical momentum, flexion-momentum time, and 3rd step stability were consistent between tasks and yielded acceptable reliability.
STW is a more challenging task due to the merging of rising with GI reflected by greater CoP-xCoM separation compared to STSW indicative of more positional instability. However, BCoM vertical momentum, flexion-momentum time, and step3 stability remained consistent in healthy individuals and are therefore candidates with which to monitor change in gait rehabilitation following pathology. Future studies should impose typical pause-durations observed in pathology upon healthy subjects to determine if the parameters we have identified remain consistent.
Humans often transition between postures as part of daily life. For example working adults are reported to rise from a seated position more than 60 times per day  and healthy individuals have been found to initiate walking from sedentary positions including siting over 90% of the time (rising-to-walk) . Whilst ubiquitous, rising-to-walk is also a flexible transitional task. It can be undertaken smoothly, as in sit-to-walk (STW) where sit-to-stand (STS) is integrated fluidly with gait-initiation (GI) . Yet it can equally be executed with increasing time between STS and GI up to where they are separated  as part of a normal dual task; for example when a seated individual rises but pauses to check their pockets before they set off walking.
The London South Bank University Ethics Committee approved this study (UREC1413/2014). Participants gave written informed consent before data collection began.
Peak BCoM momentum during rising was greater in STW in the medio-lateral (toward the stance-limb) [d = 5.073, p<0.001] and AP (anterior) directions [d = 1.667, p = 0.001], but there was no difference vertically (Table 6). Despite seat-off occurring earlier in STW (Fig 2), there was no significant difference in flexion-momentum phase-time (movement-onset to seat-off). In contrast, transition phase-time (seat-off to GI-onset) [d = 3.362, p<0.001] were both significantly shorter in STW compared to STSW [d = 3.362, p<0.001]. In addition, maximum CoP-xCoM distances were greater during step1 [d = 1.558, p = 0.001] and 2 [d = 0.961, p = 0.014] in STW, but not during step3 (Table 6). Source: http://doi.org/10.1371/journal.pone.0205346