Abstract
BACKGROUND: Rotation of the trunk about its long axis or 'body roll' is essential for maximising front crawl swimming performance yet research on how physical impairment affects body roll is extremely limited. This study quantifies body roll kinematics in swimmers with and without central motor and neuromuscular impairments (CMNI). It was hypothesised that body roll kinematics differ between CMNI and non-disabled swimmers, are associated with sport class (level of impairment) and are influenced by upper and lower-limb functional levels. METHODS: Three-dimensional motion analysis of 27 CMNI (sport classes 2-9) and 13 non-disabled competitive swimmers at 100-200 m race pace provided body roll kinematics, including shoulder and hip roll ranges and torso twist. Health conditions of the CMNI group were cerebral palsy (n = 12), spinal cord injury (n = 10) and neuromuscular disorders (n = 5). CMNI swimmers were divided into three upper-limb [mild (n = 9), moderate (n = 9), severe (n = 9)] and three lower-limb function subgroups [bilateral (n = 2), unilateral (n = 6), without kick (n = 19)] based on their Froude efficiency (a measure of how effectively upper limbs contribute to propulsion) and the number of lower limbs actively kicking during trials, respectively. RESULTS: The CMNI group exhibited lower shoulder roll range (104 ± 11° vs. 88 ± 21°, p < 0.05) and torso twist (58 ± 13° vs. 48 ± 22°, p < 0.05) but greater hip roll range (62 ± 10° vs. 75 ± 29°, p < 0.05) than the non-disabled group. Statistical non-parametric mapping revealed less shoulder roll from 0 to 28%, less hip roll from 0 to 10%, greater hip roll from 91 to 100%, and less torso twist from 15 to 32% and from 75 to 81% of the cycle, in the CMNI than the non-disabled group (p < 0.05). CMNI body roll patterns varied widely, but discrete and continuous variables did not differ between upper-limb subgroups or between lower-limb subgroups. CONCLUSIONS: CMNI swimmers exhibit different body roll patterns to non-disabled swimmers. The study findings can be used to inform Para swimming coaches and improve the sport-specificity of land-based and water-based assessments currently used to classify CMNI swimmers.