A weekly minimum of 150 minutes of moderate intensity exercise (3.0-5.9 METs) or 75 minutes of vigorous intensity exercise ([greater than or equal to] 6.0 METs), and two resistance training sessions are recommended for individuals to maintain or improve health status (ACSM, 2018). However, a recent report from the Centers for Disease Control (CDC) revealed that only about 23% of adults in the United States currently meet the minimum requirements for weekly exercise (Blackwell and Clark, 2018). In addition, the combination of inadequate physical activity and increased sedentary behaviors can lead to negative health effects for all ages, including increased risk for cardiovascular disease, stroke, metabolic disease, cancer, hypercholesterolemia, hypertension and obesity (ACSM, 2018; Bailey et al., 2017; Bakrania et al., 2016; Jenkins et al., 2017; Silfee et al., 2017; Vieira et al., 2016). Each of these diseases can impact or increase other health problems. Therefore, it is important to investigate the effectiveness of different forms of exercise in an effort to increase physical activity and decrease sedentary behaviors.
A major benefit of water exercise is the reduction of weight bearing stress on the body, which may even improve the ability to perform some joint actions (Ruoti et al., 1994), allowing diverse patient populations to have the ability to exercise. As little as five weeks of aquatic aerobic exercise has been shown to improve heart rate responses to exercise in older women (Costa et al., 2017). Water exercise can also be helpful to overweight/obese populations resulting in improvements in dyslipidemia, body composition and cardiovascular fitness (Costa et al., 2018a; 2018b; Lopera et al., 2016; Taunton et al., 1996; Vasic et al., 2019).
Interval training is another popular form of exercise which typically involves exercise performed at a higher intensity for a shorter duration of time, including rest or active recovery periods at lower intensities between the intervals. Some studies have shown that high intensity interval training (HIIT) improves cardiometabolic health to a similar degree as steady state or moderate continuous types of exercise (Fisher et al., 2015; Foster et al., 2015). Other HIIT studies have shown greater improvements in blood pressure response, blood lactate levels, heart rate, and RPE than forms of continuous training (Sosner et al., 2016; Thum et al., 2017). HIIT is also beneficial because it can be adapted for the needs of individual participants. Interval and rest durations can be adjusted to alter the intensity of the exercise. Astorino et al. (2016) examined different types of HIIT that used short sprint intervals, longer intervals, or combinations of those two interval types. They found that the combination of the two interval types led to the greatest increases in maximal oxygen consumption, stroke volume and cardiac output. Therefore, it may be beneficial to alter the interval lengths over the course of the program to increase program adherence.
Maintaining an exercise regimen is an important factor for improving physical activity and therefore, it is crucial to consider factors which affect adherence to an exercise regimen. Exercise variety, perception of health benefits, competence of facility staff, self-efficacy, and enjoyment of exercise all have a positive influence on maintaining a regular exercise program (Sylvester et al., 2016; Trost et al., 2003; Whaley and Schrider, 2005). High intensity interval training has been shown to have positive effects on exercise adherence, including improved arousal and affect, leading to greater enjoyment over the course of the exercise program (Astorino et al., 2016; Fisher et al., 2015; Heisz et al., 2016; Kong et al., 2016; Martinez et al., 2015; Thum et al., 2017). Such factors may affect the person's perception of the exercise and therefore increase exercise adherence. Water-based exercise may also improve exercise adherence from its effect on quality of life, depression, anxiety, and mood scores (Schuch et al., 2014; Wei et al., 2006). Because of the positive effects that both aquatic and HIIT exercises have on health, fitness, and exercise adherence, it is important to consider how the combination of those types of exercise could affect participants.
Aquatic HIIT (AHIIT) studies, to date, have utilized modes of exercise such as machine-based aquatic running or cycling. Aquatic running programs have led to improvements in submaximal and maximal aerobic power, maximal ventilatory capacity, resting heart rate and blood pressure, joint pain, balance, function, and mobility (Bressel et al., 2014; Broman et al., 2006; Reichert et al., 2016). Aquatic cycling programs have resulted in reductions in blood pressure and when combined with a Mediterranean diet, led to improvements in body composition, fasting glucose, triglyceride levels, blood pressure, and fitness (Boidin et al., 2015; Sosner et al., 2016). However, the aquatic treadmills and aquatic cycles used in these studies are not always readily available for public use. Therefore, it is necessary to investigate the effectiveness of simple forms of aquatic exercise such as aquatic calisthenics which are easy for individuals to perform using readily available equipment such as swim paddles and aquatic dumbbells.
The main purpose of the present study was to determine whether a short AHIIT program using aquatic-calisthenic exercises could improve cardiorespiratory fitness and body composition in sedentary, overweight young adults. The program included a variety of aquatic-calisthenic exercises that have been utilized in water aerobics classes, but for the purpose of this study, were adapted to an interval training protocol. It was hypothesized that the five-week AHIIT program using calisthenic exercises would improve cardiorespiratory fitness and body composition.
The study was approved by the institutional review board of a regional university. Eleven sedentary adults (9 females, 2 males) were recruited from university classes and completed the study (Table 1). Participants filled out a medical history questionnaire with questions regarding the number of hours they spent doing different activities including sleeping, working, eating, exercising, and driving. Each participant reported being seated or supine for 20 or more hours per day. The participants were determined to have met th e following criteria: (1) no injuries over the previous six months that would prevent them from participating, (2) a majority of time spent sedentary each day, (3) a sedentary type of job (if currently employed), and (4) no regular physical activity for three months prior to the exercise program. Before beginning the program, the participants were informed that they must complete a preliminary testing session, a familiarization session, attend three exercise training sessions per week during each week for five weeks of the study and complete a post-testing session. All procedures performed in the current study involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The study was approved by the University Institutional Review Board.
In the preliminary session, participants signed an informed consent form that outlined expectations for each session and eligibility requirements for participation, and then completed a medical history questionnaire. Once eligibility was determined, the following data were collected for each participant after 5-min rest in a seated position: heart rate via a heart rate monitor (Polar H10, Polar Electro, Kempele, Finland), blood pressure via auscultation using a hand-held sphygmomanometer and stethoscope, 3-site skinfold assessment of body composition with skinfold calipers (Lange Instruments, Santa Cruz, CA), and peak oxygen consumption (V[O.sub.2]peak) during a graded exercise treadmill test (GXT). The 3 sites anatomic points for skinfold assessment for female participants were the triceps, suprailiac, and thigh, whereas the chest, abdominal, and thigh measurements were used for male participants (ACSM, 2018). The participants were familiarized with the treadmill and breathing mask of the metabolic system before completing the graded exercise test. A modified Kraemer protocol (Kraemer et al., 2011) was used for the graded exercise test, which began with a 3-minute warm up at 1.2 mph followed by the first stage at 2.5 mph and a 4% grade elevation. Each stage lasted for 3 minutes with a 4% grade of elevation and the speed was increased by 1 mph until the participant indicated that they could not continue. Expired gases were collected and analyzed using a metabolic cart (Parvomedics, Sandy, UT). V[O.sub.2] and HR were determined using the metabolic system and HR monitor during the last 30s of stage 1 and stage 2 of the test. The last 30s of stage 1 and 2 was used to allow subjects to reach steady state. The sampling rate for expired gases was every...