Programs designed to improve cardiovascular, metabolic, and psychological health have begun to replace low-intensity exercise by repeated short-to-long bouts of high-intensity exercise with intervals of recovery [referred to as high-intensity interval training (HIIT)] (Kessler et al., 2012; Little and Francois, 2014; Elliott et al., 2015; Gielen et al., 2015; Schmitt et al., 2016). In addition to allowing an unlimited number of protocols with different work-to-rest ratios, order of loading and distribution of training intensity, HIIT requires less time than low-intensity-high-volume training, which is attractive, since lack of time appears to be one of the major reasons for not exercising (Godin et al., 1994).

In contrast to the traditional endurance-based HIIT, a relatively novel variation also called functional training/fitness incorporates multi-stimulating, circuit-like, multiple-joint, high-intensity training (Circuit_HIIT), and becoming of increasing interest to fitness enthusiasts (Buckley et al., 2015). Such exercise more related to strength can improve body composition (Sillanpää et al., 2009; Neves et al., 2017), as well as cardiovascular (Shaw and Shaw, 2009; Ho et al., 2012a,b), metabolic (Schumann et al., 2014; Neves et al., 2017) and functional fitness (Neves et al., 2017) in physically inactive individuals and, in addition, at least in older individuals, certain aspects of quality of life (Sillanpää et al., 2012). However, with increasing exercise intensity, enjoyment declines, and the excessive demands made by HIIT have been proposed to diminish intrinsic motivation and discourage adherence to further exercise (Hardcastle et al., 2014).

Strength exercise such as Circuit_HIIT, is well known to elevate muscle mass and thereby potentially reduce numerous risk factors for cardiovascular disease (Hurley et al., 1988; Poehlman et al., 2000). In contrast, low-intensity endurance exercise is known to augment plasma volume (Green et al., 1987, 1990), muscular blood flow (Coyle, 1999), and capillary and mitochondrial densities (Hoppeler and Weibel, 2000) thereby improving peak oxygen uptake (Hickson et al., 1981). Improved cardiorespiratory fitness (e.g., maximum oxygen uptake) has been associated with improved health and less premature death (Bouchard et al., 2015). Due to the different responses evoked, functional strength training in the form of Circuit_HIIT combined with low-intensity endurance exercise (Circuit_combined) may lead to synergistic improvements in cardio-respiratory and metabolic parameters, body composition, functional strength and quality of life, which, to the best of our knowledge, has not yet been investigated in detail with respect to overweight women.

Accordingly, we compare here the psycho-physiological responses of physically inactive women performing a multi-stimulating, circuit-like, multiple-joint conditioning program (Circuit_HIIT), or the same program in combination with low-intensity high-volume exercise (Circuit_combined). On the basis of the responses discussed above, our hypothesis was that Circuit_HIIT improves functional strength and metabolic parameters as well as body composition, but may at the same time impair quality of life, whereas Circuit_combined improves cardio-respiratory and metabolic parameters and quality of life.

The women in the Circuit_HIIT and Circuit_combined groups completed 89 ± 5 and 90 ± 6% of the planned training sessions, respectively. Their pre- and post-values with statistical analysis are documented in Tables 2–5.

Body mass, body-mass index, waist-to-hip ratio and fat mass declined and fat-free mass increased to the same extent in both groups (Table 2).

Ratings of perceived exertion following either intervention were lower than at baseline. Peak oxygen uptake improved to a greater extent following Circuit_HIIT than Circuit_combined (Table 3).

The number of push-ups, burpees, one-legged squats and 30-s skipping, as well as the counter-movement jumping height improved after both Circuit_HIIT and Circuit_combined, with no differences between these groups (Table 3). The number of leg-levers was improved to a greater extent by Circuit_HIIT than Circuit_combined (Table 4).

Physical and social functioning, vitality, role of emotional limitations and mental health improved following both Circuit_HIIT and Circuit_combined (Table 5). However, perception of physical pain was higher only after Circuit_HIIT and perception of general health was enhanced only by Circuit_combined.

The major findings of this comparison of several psycho-physiological responses of overweight women to 9 weeks of either Circuit_HIIT or Circuit_combined were as follows:

With Circuit_HIIT, perception of physical pain and peak oxygen uptake both rose to a greater extent.

Numerous investigations have focused on the effect of HIIT on parameters of cardio-respiratory fitness including VO_2peak (Stoggl and Sperlich, 2014; Schmitt et al., 2016; Zinner et al., 2016). Since this value limits ATP production via oxidative phosphorylation and is thus strongly associated with cardiorespiratory fitness, as well as general health and premature death, it is frequently utilized as an integrative indicator of cardiopulmonary fitness (Bassett and Howley, 2000; Bouchard et al., 2015). Here, peak oxygen uptake was improved after 9 weeks with 3 weekly sessions of either Circuit_HIIT (10.1%) or Circuit_combined (4.4%). The overall greater response of VO_2peak to high-intensity exercise can be explained by better central adaptation, including augmented plasma and blood volumes (Convertino et al., 1980; Green et al., 1987; Graham et al., 2016) with elevated stroke volume (Green et al., 1990; Goodman et al., 2005).

From this point of view, we may conclude that three sessions of Circuit_HIIT enhance VO_2peak more effectively than two sessions of Circuit_HIIT and one session of low-intensity exercise (Circuit_combined).

The Circuit_HIIT participants performed primarily resistance training (i.e., squats, lunges, push-ups, etc.) in combination with repeated sprints, with very little rest between these exercises. Although this regimen was more related to strength, the women enhanced their cardiorespiratory fitness (i.e., oxygen uptake) to an extent similar to that observed with earlier circuit-based exercise (Gettman et al., 1982; Beckham and Earnest, 2000). A 7–12% increase in peak oxygen uptake following 4–12 weeks of body weight circuit training is consistent with previous reports (Gettman et al., 1982; McRae et al., 2012). However, our present observations reveal that 3 weekly sessions of Circuit_HIIT improve peak oxygen uptake in a time-effective manner.

Circuit_combined consisted of two of the weekly Circuit_HIIT sessions and an additional weekly session of high-volume exercise (60–105 min at approximately 65% of peak oxygen uptake). In the case of well-trained endurance athletes a combination of HIIT and high-volume low-intensity exercise might be more beneficial than either alone, since a) low-intensity endurance exercise (<2 mM blood lactate or ~55–85% peak heart rate) allows the body to recover sufficiently and b) excess HIIT may exert a negative impact on the autonomic nervous system (Chwalbinska-Moneta et al., 1998; Esteve-Lanao et al., 2007). Although the combination of low-volume, high-intensity exercise and high-volume, low-intensity exercise (so-called polarized intensity distribution) led to greater improvements in selected endurance values for elite endurance athletes (Stöggl and Sperlich, 2015), our present findings indicate that this is not the case for overweight women performing multi-stimulating, circuit-like, multiple-joint training together with high-volume low-intensity exercise (Circuit_combined).

In the current investigation, the women in the Circuit_HIIT group perceived more pain, with no change in perception of general health. High-intensity strength training with eccentric components such as those involved in multi-stimulating, circuit-like, multiple-joint training induces muscle soreness. Although in general in adults, perception of muscle pain is attenuated as training proceeds, (Levinger et al., 2007), the women in the Circuit_HIIT group perceived more pain after the 9-week intervention. The injury rate associated with multi-stimulating, circuit-like, multiple-joint training is approximately 20% (Weisenthal et al., 2014), but none of the women in either of our groups mentioned any injury. However, elevated pain in connection with HIIT may discourage untrained individuals from performing regular physical activity (Hardcastle et al., 2014; Del Vecchio et al., 2015), although previous studies showed no effect of high-intensity exercise on perceived pain in female patients (Schmitt et al., 2016). Further studies are needed to clarify the effect of high-intensity training, especially short- and long-term, on perceived pain. However, Circuit_HIIT and Circuit_combined induced improvements in several dimensions of quality of life, which are perhaps the most important reasons to continue training. To summarize, in the present investigation Circuit_combined appears to have augmented certain aspects of quality of life somewhat more, because there was no enhanced perception of pain.

Nine weeks of multi-stimulating, circuit-like, multiple-joint training involving either Circuit_HIIT or Circuit_combined improved the body composition, selected variables of functional strength and certain dimensions of quality of life in overweight women. Circuit_HIIT also improved peak oxygen uptake, but with more perception of pain. Circuit_combined appears to improve perception of general health to a greater extent than Circuit_HIIT.

BS, BWS, CZ, VVS, HL, HCH designed and approved the methods, analyzed data, and assisted in manuscript writting. BS, VVS, HL, CZ performed data collection.