Quantifying the acute responses of shallow-water immersion on walking physiology and biomechanics: a systematic review and meta-analysis

Shallow water walking (SWW) generates changes in cardiorespiratory parameters in comparison to terrestrial exercise, and these changes are highly dependent of immersion depth. We reviewed the evidence from observational studies focusing on physiological and biomechanical responses of SWW in comparison to dry land walking. This systematic review and meta-analysis (initial search: 1516 studies; systematic review: 40 studies; meta-analysis: 22 studies) presents evidence that higher energy expenditure, heart rate and rating of perceived exertion are accompanied by depth-dependent reductions in self-selected speed and stride length in SWW compared with dry land. The stride frequency, however, was similar at waist and reduced at xiphoid depth. As expected, the ground reaction forces were reduced according to the buoyance forces acting. SWW appears to increases muscular activity. Importantly, the depth-related increase in energy expenditure of SWW seems to involve a major role of resistive forces compensating the reduced task of support the body weight. Besides the benefits of water immersion as reduced joint impact and safety, biomechanical alterations on force production may produce additional long-term gains in functional mobility. However, the influence of these physiological and biomechanical alterations on functional mobility are largely unknown. Due to these inconclusive points, there is a huge opportunity to determine (1) the alterations on muscle activation in different depths in order to explain the higher energy expenditure at organismal level, and (2) whether these alterations can maximize gains in metabolic economy and gait biomechanics after long-term SWW intervention. PROSPERO registration protocol: CRD42018113040.