High-intensity interval training (HIIT) has emerged as an attractive alternative to traditional continuous exercise training (CT) programs for clinical and healthy populations who find that they can achieve equal or greater fitness benefits in less time. Land-based HIIT may not be an appropriate choice for some participants. Few studies have explored the acute responses and chronic adaptations of HIIT in an aquatic environment, and no study has compared the cardiometabolic responses of an aquatic-based program to a land-based HIIT program. Shallow-water aquatic exercise (AE) programs utilizing HIIT have elicited comparable and, in some cases, greater physiological responses compared with constant-intensity or continuous AE regimens. Factors that may explain why HIIT routines evoke greater cardiometabolic responses than CT protocols may be based on the types of exercises and how they are cued to effectively manipulate hydrodynamic properties for greater intensities. Favorable aquatic HIIT protocols such as the S.W.E.A.T. system may serve as a beneficial alternative to land-based HIIT programs for clinical, and athletic populations, potentially reducing the likelihood of associated musculoskeletal and orthopedic complications. Hence, the purpose of this review is to examine the role of AE as an alternative safe and effective HIIT modality.

Purpose: To evaluate if sedentary time (ST) is associated with heart rate (HR) and variability (HRV) in adults. Methods: We systematically searched PubMed and Google Scholar through June 2020. Inclusion criteria were observational design, humans, adults, English language, ST as the exposure, resting HR/HRV as the outcome, and (meta-analysis only) availability of the quantitative association with variability. After qualitative synthesis, meta-analysis used inverse variance heterogeneity models to estimate pooled associations. Results: Thirteen and eight articles met the criteria for the systematic review and meta-analysis, respectively. All studies were cross-sectional and few used gold standard ST or HRV assessment methodology. The qualitative synthesis suggested no associations between ST and HR/HRV. The meta-analysis found a significant association between ST and HR (β = 0.24 bpm per hour ST; CI: 0.10, 0.37) that was stronger in males (β = 0.36 bpm per hour ST; CI: 0.19, 0.53). Pooled associations between ST and HRV indices were non-significant (p > 0.05). Substantial heterogeneity was detected. Conclusions: The limited available evidence suggests an unfavorable but not clinically meaningful association between ST and HR, but no association with HRV. Future longitudinal studies assessing ST with thigh-based monitoring and HRV with electrocardiogram are needed.

Aquatic exercise (AE) is a popular form of physical activity, yet few studies have assessed the individual's energy expenditure (EE) associated with a continuous bout of AE. Studies using indirect calorimetry to measure EE have reported limitations associated with test methodology and the ability to control individual's exercise intensity or tempo. To evaluate EE and cardiorespiratory (CR) responses during a 40-minute shallow-water AE session in young adult women. Twenty-one healthy women (aged 21.7 ± 3.4 years) completed an orientation practice session and a 40-minute shallow-water AE session using a traditional exercise class format and the SWEAT video-based instructional cuing program. The high-intensity interval format included the following segments: 1) warm-up (3 minutes); 2) CR segment ( 22 minutes); 3) muscular endurance segment (ME; 10 minutes); and 4) cool-down (5 minutes). Subject oxygen consumption (VO2; mL/kg/min), heart rate (HR) and OMNI overall ratings of perceived exertion (RPE-O) were assessed each minute. Average kcal/min1, metabolic equivalents (METs; 1 MET = 3.5 mL/kg/min), and total kcals per segment and for the overall session were calculated. The total subject EE throughout the 40-minute trial (including warm-up and cool-down segments) was 264 kcals, with an overall average of 6.3 kcals/min (5.6 METs).The average kcals/min expended throughout CR segments 2 through 6 was 8.05 (7.1 METs), with the Hoverjog segment producing the greatest average kcals/min at 8.3 (7.3 METs). The CR portion (22 min) contributed 65% of the total EE (171 kcals) of the 40-minute AE trial. For the overall AE trial, the highest and average subject VO2 achieved were 33.3 and 19.7 mL/kg/min, respectively. The average highest subject heart rate achieved was 177 beats per minute (bpm), equivalent to 90% of the participant's age-predicted HRmax. Energy expenditure during a 40-minute AE session met national recommendations for a daily moderate-to-vigorous bout of physical activity offering a viable alternative to land-based exercise. Because AE serves as a partial-weight bearing modality, future studies are needed to clarify the EE of shallow-water AE in apparently healthy and clinical populations.

Consistent differences between males and females have been shown in land-based measurements of anaerobic power and capacity. However, these differences have not been investigated for a tethered 30-s maximal swimming test (TST). The purpose of this study is to explore gender differences in land and pool-based assessments of anaerobic power (F_peak) and capacity (F_mean), as well as the influence of body composition. Thirteen males and fifteen females completed land (Wingate (WAnT)) and pool-based (TST) measures of anaerobic power and capacity previously described in the literature. Additionally, the subjects completed assessments of body composition via air displacement plethysmography. The males produced higher force than the females for F_peak (p < 0.001) and F_mean (p = 0.008) during the TST. However, linear regression analysis determined that lean mass significantly predicted F_peak (p = 0.002) and F_mean (p < 0.001) during the TST, while gender was no longer significant (p = 0.694 and p = 0.136, respectively). In conclusion, increases in anaerobic power and capacity (F_peak and F_mean) may be a function of increased lean mass in males and females, warranting future research on the impact of resistance training programs on force production and swimming performance.

Nagle, EF, Sanders, ME, Gibbs, BB, Franklin, BA, Nagle, JA, Prins, PJ, Johnson, CD, and Robertson, RJ. Reliability and accuracy of a standardized shallow water running test to determine cardiorespiratory fitness. J Strength Cond Res 31(6): 1669–1677, 2017—A standardized fitness assessment is critical for the development of an individualized exercise prescription. Although the benefits of aquatic exercise have been well established, there remains the need for a standardized nonswimming protocol to accurately assess cardiorespiratory fitness (CRF) in shallow water. The present investigation was designed to assess (a) the reliability of a standardized shallow water run (SWR) test of CRF and (b) the accuracy of a standardized SWR compared with a land-based treadmill (LTM) test. Twenty-three healthy women (20 ± 3 years), with body mass index (23.5 ± 3 kg·m⁻²), performed 2 shallow water peak oxygen consumption (V̇o ₂peak) running tests (SWRa and SWRb), and 1 V̇o ₂max LTM. Intraclass correlation coefficients indicated moderately strong reliability for V̇o ₂peak (ml·kg⁻¹·min⁻¹) (r = 0.73, p < 0.01), HRpeak (b·min⁻¹) (r = 0.82; p < 0.01), and O₂pulse (V̇o ₂ [ml·kg⁻¹·min⁻¹]·HR [b·min⁻¹]) (r = 0.77, p < 0.01). Using paired t-tests and Pearson's correlations, SWR V̇o ₂peak and HRpeak were significantly lower than during LTM (p ≤ 0.05) and showed moderate correlations of 0.60 and 0.58 (p < 0.001) to LTM. O₂pulse was similar (p > 0.05) for the SWR and LTM tests with a moderate correlation of 0.63. A standardized SWR test as a measure of CRF is a reliable, and to some degree, valid alternative to conventional protocols and may be used by strength and conditioning professionals to measure program outcomes and monitor training progress. Furthermore, this protocol provides a water-based option for CRF assessment among healthy women and offers insight toward the development of an effective protocol that can accommodate individuals with limited mobility, or those seeking less musculoskeletal impact from traditional land-based types of training.