Author(s): CARPENTIER, M., NOISET, M., FAORO, V., Institution: UNIVERSITÉ LIBRE DE BRUXELLES - ULB, Country: BELGIUM, Abstract-ID: 2426

INTRODUCTION:
Running sports often lead to lower limb mechanical injuries. Unloaded training, such as indoor cycling (IC), are often advised during recovery, to limit cardio-pulmonary capacity deconditioning with limited mechanical stress(1). Deep water running (DWR) is an alternative training method to reduce low-limb overload, improve muscle strength(2) and balance(3), with greater muscular forces than in air(4). While validated DWR training protocols still need to be established, we compared the cardio-pulmonary response during exercise sessions of DWR vs IC. It also remains unclear if sessions need to be calibrated on heart rate (HR) or oxygen consumption (VO2).
METHODS:
15 healthy active subjects were enrolled in the study; 22±3 yo, 53% women, 43±7 ml/min/kg maximal VO2 measured during cyclo-ergometric cardio-pulmonary exercise test (CPET) which also allowed determination of HR and VO2 at the first ventilatory threshold (VT1). All subjects performed randomly one IC and DWR continuous exercise session calibrated on HR at VT1 (respectively IC(HR) and DWR(HR)) consisting of: 5-minutes warm-up at 80% of heart rate (HR) at the first ventilatory threshold (VT1), followed by 2 sets of 10 minutes at 100% HR@VT1 separated by 2 minutes rest. A subgroup of 7 subjects performed an additional DWR session calibrated by VO2 at VT1 (DWR(VO2)). HR, ventilation (VE) and gas exchange were measured continuously during CPET and DWR/IC sessions, with blood lactate levels measured 30s after exercise. When comparing DWR(HR) with DWR(VO2) values are given as med [Q1; Q3].
RESULTS:
At identical exercise HR, VO2 was higher during DWR(HR) (38±9 ml/min/kg; 88% of VO2max) as compared to IC(HR) training (31±6 ml/min/kg; 72% of VO2max, p<0.0001) as well as VE (DWR(HR) : 74±2 L/min, 60% of VEmax vs IC(HR) : 54±6 L/min, 36% of VEmax, p<0.0001) with no difference in lactate concentrations (DWR(HR) : 3.9±1.7 mmol/L, vs IC(HR) : 3.6±2 mmol/L). Higher VE (p=0,047) (DWRHR : 80 [57; 84] L/min, DWR(VO2): 50 [44; 55] L/min) and higher HR (p=0,047) (DWRHR : 143 [138; 157] bpm, DWR(VO2) : 113 [99; 158] bpm) were observed during DWR(HR) compared to DWR(VO2), with a greater respiratory exchange ratio (RER) for DWR(HR) (p=0,03) (0.92 [0.86; 0.96] vs. 0.81 [0.75; 0.88]) but with no difference in lactate concentrations (DWR(VO2) : 2.7 [1.1; 2.9] mmol/L).
CONCLUSION:
DWR(HR) reaches higher exercise intensity, as measures by VO2 and VE levels, compared to IC(HR), but with identical lactate production. This is likely attributed to the chronotropic response of hydrostatic pressure inherent in DWR, which enhances venous return and stroke volume. The validation of this hypothesis through DWR(VO2) underscores the necessity of acquiring detailed knowledge regarding the physiological effects of each exercise modality. It seems therefore important to consider accurately adapting DWR training programs to meet specific performance objectives and optimize training/rehabilitation outcomes.
1 Glass, 2 Foley, 3 Simmons, 4 Miyoshu