Aim: This study was designed to assess submaximal cardiac and pulmonary demand imposed by walking on a non motorized treadmill in land and in water condition.
Methods: Eight healthy young subjects (mean age, body mass and height: 26.5 ± 2.8 years; 66.7 ± 9.60 kg; 172 ± 8.07 cm) performed one maximal treadmill running test on land and a submaximal incremental test (treadmill speed 2, 3, 4 km.h-1; 5 minutes step duration; 15 minutes total duration) in land (L) at 2, 3, 4 km.h-1 (L2, L3, L4) and in water (W) at 2, 3, 4 km.h-1 (W2, W3, W4). Individual stride frequency at any given submaximal walking speed on land was used to perform comparable water tests. Heart rate (HR) and oxygen consumption (VO₂) were continuously measured during the tests.
Results: Rest heart rate (%max) decreased immediately after water immersion [land HR(%max) 42 b.min-1±3; water HR(%max) 36 b.min-1 ± 5, P<0.05] while the other physiological parameters were comparable between land and water condition [land VO2(%max) 9.44 mL.Kg.min-1 ± 1.54; water VO₂(%max) 7.75 ml.Kg.min-1 ± 2.4, p>0.05; land ventilation [VE(%max)] 8.71 L.min-1 ± 2.37; water VE(%max) 7.67 L.min-1 ± 2.79, p>0.05; land respiratory exchange ratio (RER) 0.77 ± 0.5 water RER 0.75 ± 0.07, P>0.05]. During exercise at 2, 3 and 4 Km.h⁻¹, reserve heart rate [HRR (%max)] was higher during water walking (W2 35 ± 10; W3 54 ± 11; W4 76 ± 9 b.min⁻¹) than during land walking (L2 23 ± 5; L3 39 ± 7; L4 58 ± 8 b.min-1, P<0.05). VO₂and VE were not different.
Conclusion: The findings suggest that water walking on a non motorized treadmill elicits similar VO₂but higher HR than land walking; this factor should be considered when prescribing exercise intensity in water using heart rate.