Regular exercise is well known to improve health and reduce a number of risk factors for chronic disease (7). Typically, participation in exercise follows a traditional approach of separate resistance and aerobic exercises. This combination of exercise training modalities improves body composition and cardiovascular fitness in both sedentary and overweight populations (20,21,34,36). Despite the health benefits, approximately 47% of Canadian adults fail to participate in physical activity more than 1 day a week and 85% do not meet Canada's new physical activity recommendations (12). Potential reasons for this lack of participation in physical activity include barriers such as accessibility to gym equipment or a fitness facility or lack of time (18,23). Furthermore, many people view physical activity itself as time consuming, in addition to other time-consuming factors such as travel time to a fitness facility. These barriers deter people from performing physical activity, preventing positive benefits (10,22).
Although not time effective, alternative forms of exercise training have been used to improve fitness such as circuit training. Typical circuit training involves the use of resistance training exercise carried out with external loads performed in succession with little rest periods between exercises (31). This style of training however does not address the time-component, as exercise sessions are similar to combined resistance and aerobic training sessions. Although high-intensity interval training has gained in popularity recently due to its time-efficient and effective training sessions for improving aerobic/anaerobic fitness and health (15,24,25), these time-efficient but intense workouts include supramaximal efforts using running and cycling as modes of exercise. Whether using repeated body weight resistance training exercises with little to no rest periods over a similarly time-efficient workout would improve both cardiovascular fitness and muscular strength/endurance is not well understood.
Recently, it was demonstrated that single-set whole-body aerobic resistance training (8 sets of 20-second intervals with 10-second rest between sets over 4 weeks; Tabata protocol) using body weight exercises with light external loads improved cardiovascular fitness in recreationally active females similar to traditional endurance training, but only the interval group improved muscular endurance (27). This high-intensity exercise format can be tailored to many exercise protocols and can be performed without fitness equipment by performing specific body weight exercises (i.e., squats, lunges, and burpees) in succession with only small breaks between exercises or between sets of exercises. Nonetheless, the previous study did not compare the interval workout to a combination of resistance and aerobic training. Therefore, whether whole-body aerobic resistance training can improve aerobic/anaerobic fitness and muscle strength/endurance similar to traditional resistance training combined with aerobic training is currently unknown. The purpose of this study was to determine whether a time-effective whole-body aerobic resistance training circuit is as effective as traditional resistance training combined with aerobic exercise in improving aerobic and anaerobic fitness, as well as muscular strength and endurance in young sedentary females.
Experimental Approach to the Problem
Participants completed 5 weeks of training (3 times per week). Pre- and post-training measures included a V[Combining Dot Above]O2peak test, 30-seccond anaerobic Wingate cycle test, and muscular strength/endurance tests for the chest, back, quadriceps, and hamstrings muscles. Pretraining testing was completed in 2 sessions over 1 week separated by at least 48 hours. After pretesting, participants were assigned to one of the 2 groups: (a) whole-body aerobic resistance training circuit group (CIRCUIT) or (b) traditional resistance training combined with aerobic exercise (COMBINED) based on their pretraining V[Combining Dot Above]O2peak and muscular strength. Posttraining testing began 72 hours after the final training session to eliminate any acute exercise effects and was completed in 2 sessions separated by at least 48 hours identical to pretesting.
Thirty-four healthy sedentary females (n = 34; 20.9 ± 3.2 years; age range was 18–29 years; 167.9 ± 6.5 cm; 68.0 ± 15.2 kg; mean ± SD) volunteered to participate in this study. All participants were healthy as assessed by the PAR-Q health questionnaire (38) and all were deemed sedentary based on their self-reported habitual physical activity, which consisted of ≤2 sessions per week of structured exercise for ≤30 minutes per session according to both the American College of Sports Medicine (13) and the Canadian Society for Exercise Physiology (39). Participants were instructed to maintain their regular dietary habits for the duration of the study. Before any participation, the experimental procedures were explained fully to each participant and all provided written informed consent. The University of Lethbridge Human Subjects Research Committee approved this study.
Each participant completed a laboratory familiarization session to introduce all testing procedures and ensure that any learning effect was minimal for baseline measures. Participants also performed the exercises that they would be performing during training to ensure they learned proper form. Participants performed repetitions of each exercise with a light amount of weight (5–7.5 kg) for the resistance exercises or with their own body mass for the circuit exercises. At the end of this session all participants were comfortable performing each exercise with proper form and cadence.
All participants were instructed to refrain from consuming alcohol or caffeine within 24 hours of pretesting and to refrain from any physical activity in that time frame. Height and body mass were measured using a physician beam scale (Healthometer; Sunbeam Products, Florida, USA). Participants completed: (a) a cycling V[Combining Dot Above]O2peak test to measure cardiorespiratory fitness, (b) a 30-second Wingate cycle tests, (c) predicted 1 repetition maximum (1RM) testing, and (d) muscular endurance testing. V[Combining Dot Above]O2peak and the Wingate were completed in the same session with V[Combining Dot Above]O2peak performed first followed by the Wingate test after 15-minute recovery period. Muscular strength and endurance were completed in a separate session, with strength completed first and endurance completed after a 15-minute recovery period. We determined through pilot testing on 6 sedentary individuals who performing the 30-second Wingate tests after the V[Combining Dot Above]O2peak test first and 15 minutes of rest resulted in no differences in relative peak power output, relative average power output, relative minimum power output, or fatigue index (data not shown). Participants were required to wait at least 48 hours between pretesting sessions.
- V[Combining Dot Above]O2peak cycle ergometer test—an incremental test to exhaustion on a mechanically cycle ergometer (model 874-E; Monark Exercise, Stockholm, Sweden) was used to determine V[Combining Dot Above]O2peak using an online breath-by-breath gas collection system (Quark CPET; Cosmed, Chicago, IL, USA). Before testing, gas analyzers were calibrated using a 3-L syringe and compressed gas of a known concentration. After a 5-minute warm-up at resistance of 1 kg and 70 rpm (∼70 W), an additional 0.5-kg resistance was added (∼35 W) every 2 minutes until 70 rpm could no longer be maintained or volitional fatigue. Verbal encouragement was provided throughout the test. Attainment of V[Combining Dot Above]O2peak was verified by a respiratory exchange ratio value greater than 1.1 or by achieving age-predicted HRmax (220-age). We did not consistently observe a plateau in V[Combining Dot Above]O2 during the incremental protocol.
- Wingate anaerobic cycle test—a 30-second Wingate anaerobic cycle test (5) using a mechanically braked cycle ergometer (model 874-E; Monark Exercise) against a resistance equivalent to 7.5% of their body mass was used to determine anaerobic power output. Instructions to begin pedaling as fast as possible against the inertial resistance of the ergometer were given and the appropriate load was applied instantaneously (within 3 seconds). Verbal encouragement was provided for the remainder of the 30-second test. Peak power (highest output over any 5 seconds), average power (over the entire effort), and minimum power (lowest output) were determined using an online data-acquisition system (SMI power version 5.2.8; SMI optosensor, St. Cloud, MN, USA). Fatigue index (%) was also calculated using the following formula:
- Predicted 1RM testing—for the purposes of this study, 1RM was defined as the maximum weight a participant could lift in a given exercise with good form through the full range of motion with no help. Participants performed a predicted 1RM (30) to measure muscular strength for chest (vertical bench), back (wide-grip lat pulldown), quadriceps (leg extension), and hamstrings (leg curl) muscles due to lack of familiarity with exercise techniques. All exercises were performed using resistance exercise machines (Life Fitness Strength, Rosemont, IL, USA). Briefly, participants warmed up with 5 minutes of light aerobic exercise followed by the exercises at a low resistance (weight they could lift comfortably for 12–15 repetitions). Predicted 1RM testing then initiated with participants lifting 2 different sets of submaximal loads (8). Participants lifted 2 sets, 1 with 3–5 repetitions to fatigue, and the other with 5–10 repetitions to fatigue. The weights lifted in the 3–5 repetition set (SM1) and the 5–10 repetition set (SM2) as well as the number of repetitions performed in each set (REP1 and REP2) were used in the following formula was used to predict 1RM strength (8):
- Muscular endurance—muscle endurance was defined as the maximal number of repetitions that could be lifted at 60% of their 1RM weight with full range of motion and no help for each muscle tested for strength.
Posttesting was identical to baseline testing with at least 48 hours between testing sessions, and started 72 hours after the final training session and was completed within 10 days of the final training session. Testing occurred at the same time of day as the pretraining measures.
The first training session took place at least 48 hours after the last pretraining testing session. Training occurred 3 times per week (Monday, Wednesday, and Friday) for a duration of 5 weeks (15 sessions in total). All training sessions were supervised. At the beginning of each week, participants were provided with their weekly training program and met with study investigators to go through the training protocol and ensure proper technique for their specific exercises. Before each exercise session, participants performed a 10-minute warm-up of light aerobic exercise.
Whole-Body Aerobic Resistance Training Circuit Group
There were 5 different exercise routines (Table 1) completed in the circuit training group. Each exercise routine was completed for 1 week (3 sessions). Participants completed as many cycles of the routine as possible in 30 minutes. Specified repetitions of the specific exercise were completed before moving onto the next exercise. Exercises were chosen for simplicity with no need for equipment and to mimic similar muscle groups targeted in the COMBINED group. Participants were encouraged to take as little rest as possible in these break periods to ensure a high-intensity workout. The exercise programs were modified from week to week to try and maintain interest on behalf of the participants.
Traditional Resistance Training Combined With Aerobic Exercise Group
There were also 5 different exercise routines (Table 2) completed in the traditional training group. Each routine was performed for 1 week (3 sessions). These training sessions had participants perform resistance training for 2–3 sets at ∼50–70% 1RM for each exercise with 12–15 repetitions. All exercises were performed on machines (Life Fitness Strength) with 1-minute rest periods between each set. After completing the resistance training portion, participants completed 15 minutes of aerobic exercise at 80% of age-predicted maximal heart rate. This aerobic exercise was performed on an elliptical, cycle ergometer, or treadmill. Overall, training session duration was 45 minutes with 30 minutes of resistance exercise followed by 15 minutes of aerobic exercise. Workout logs were used to record sets and repetitions allowing supervisors to make sure repetition ranges were adhered to. Weights were increased when participants lifted above 15 repetitions and lowered if they completed less than 12. Similarly to the CIRCUIT group, adjustments were made in the exercise programs each week to try maintaining interest on behalf of the participants.
Statistical analyses were performed using Sigma Stat for Windows (version 3.5). After testing for normality and variance homogeneity, 2-way (treatment × time) repeated-measures analysis of variance (ANOVA) was used to test significance among groups pre- and post-training, with Tukey's post hoc testing, where necessary. For muscular endurance, a 1-way ANOVA was also performed to compare number of repetitions between groups at each time point. The significance level was set at p ≤ 0.05. All data are presented as mean ± SD.
There were no significant differences between groups in any variable pretesting. Both groups were similar in age, height, and body mass pretraining (CIRCUIT: 21.7 ± 2.9 years; 168.4 ± 6.3 cm; 68.5 ± 12.2 kg; COMBINED: 20.0 ± 3.4 years; 166.8 ± 6.7 cm; 67.4 ± 18.0 kg). There were no differences in body mass between groups (p = 0.926) or from pre- to post-training (p = 0.126) or in height between groups (p = 0.786) or from pre- to post-training (p = 0.996). Of the 34 participants recruited, 32 completed the training. Two participants withdrew from the study, 1 in each group (1 due to injury and the other due to sickness). Overall, attendance across both training groups was 93% with missed sessions due to other commitments (school, work) or illness.
Aerobic Fitness (VO2peak)
There was a significant interaction with time (training group vs. time; p = 0.018). V[Combining Dot Above]O2peak increased 11% (3.6 ml·kg−1·min−1; p = 0.015) in the CIRCUIT group (Figure 1). There was no change in the COMBINED group (p = 0.375).
Anaerobic Fitness (Wingate Cycle Test)
There was no significant interaction with time for relative peak power output (training group vs. time; p = 0.986), but there was a main effect of time (p = 0.004) where both CIRCUIT (5.0%; p = 0.027) and COMBINED (5.3%; p = 0.025) improved (Figure 2A). There was no interaction with time for relative average power output (p = 0.826), but there was a main effect of time (p < 0.001) where both CIRCUIT (3.2%; p = 0.006) and COMBINED (5.1%; p = 0.003) improved (Figure 2B). There was no interaction with time for relative minimum power output (p = 0.611), but there was a main effect of time on relative minimum power output (p = 0.012) where only CIRCUIT (7.5%; p = 0.031) improved with training (COMBINED; p = 0.135; Figure 2C). There was no interaction with time (p = 0.761), no main effects for training (p = 0.930), or for time (p = 0.726) with fatigue index (Figure 2D).
There was no significant interaction with time for chest strength (training group vs. time; p = 0.214), but there was a main effect of time (p < 0.001) where both CIRCUIT (20.6%; p = 0.011) and COMBINED (35.6%; p < 0.001) improved (Figure 3A). There was no interaction with time for back strength (p = 0.678), but there was a main effect of time (p = 0.004) where COMBINED improved (11.7%; p = 0.017) but CIRCUIT did not (p = 0.137; Figure 3B). There was no interaction with time for quadriceps strength (p = 0.308), but there was a main effect of time (p = 0.003) where only COMBINED (9.6%; p = 0.006) improved with training (CIRCUIT; p = 0.137; Figure 3C). There was no interaction with time for hamstrings strength (p = 0.581), but there was a main effect for time (p < 0.001) where both CIRCUIT (8.3%; p = 0.022) and COMBINED (10.2%; 0.004) improved (Figure 3D).
There was no significant interaction with time for chest endurance (training group vs. time; p = 0.367), and there were no main effects for group (p = 0.766) or time (p = 0.668; Table 3). There was no significant interaction with time for back endurance (training group vs. time; p = 0.670), but there was a main effect for time (p = 0.022) where both groups performed fewer repetitions at their current 60% 1RM weight (p < 0.047; Table 3). There was no significant interaction for quadriceps endurance (p = 0.911) and no main effect for group (p = 0.271) or time (p = 0.233; Table 3). There was no significant interaction with time for hamstrings endurance (training group vs. time; p = 0.330), but there was a main effect for time (p = 0.030) where the CIRCUIT group performed less repetitions posttraining (p = 0.046), whereas there was no difference compared with pretraining in the COMBINED group (p = 0.676; Table 3). However, comparing the number of repetitions lifted pretesting compared with posttesting revealed that the COMBINED group lifted more repetitions of their current 60% 1RM weight posttesting for the back (p = 0.006) and hamstrings (p = 0.005) vs. the CIRCUIT group (Table 3).
The purpose of this investigation was to compare the effect of a whole-body aerobic resistance training circuit (CIRCUIT) using only body weight exercises to a traditional resistance training combined with aerobic exercise program (COMBINED) on aerobic and anaerobic fitness, as well as muscular strength and endurance in young sedentary females. The CIRCUIT program was time efficient compared with the COMBINED program as it was only 2/3 the time. The main findings are (a) the body weight CIRCUIT program increased aerobic fitness, whereas the COMBINED training did not; (b) both training programs improved anaerobic fitness (relative peak power output and relative average power output), although only the CIRCUIT group increased relative minimum power output; and (c) both groups improved muscular strength for the chest and hamstring muscles, whereas only the COMBINED improved back and quadriceps strength. Neither group improved muscular endurance and actually performed less repetitions posttraining for back and hamstrings, although the COMBINED group performed more repetitions compared with the CIRCUIT group.
An 11% increase in cardiorespiratory fitness after 5 weeks of body weight CIRCUIT training in sedentary females provides evidence for the time-effectiveness of a whole-body aerobic resistance training program using only body weight exercises in sedentary females. Our participants performed primarily resistance training exercises (i.e., squats, lunges, push-ups, etc.) with little to no rest between exercises and sets and still improved cardiorespiratory fitness, similar to previous research on circuit-based training (6,14,27,28,37). It should be noted that while our participants did not complete a large amount of low-intensity cardiovascular exercise (i.e., traditional endurance exercise), they did complete small amounts at supramaximal intensity and this type of training has consistently demonstrated increases in cardiovascular measures (16,25). In contrast, the COMBINED training group did not undergo an increase in V[Combining Dot Above]O2peak, which is perhaps not surprising. Fifteen minutes of aerobic exercise training at 80% maximum heart rate, 3 times per week for 5 weeks, may be insufficient to evoke positive adaptations in cardiorespiratory fitness, even in previously sedentary females. Although a previous study has demonstrated that combined aerobic and resistance training can impair cardiorespiratory adaptations (17), others using both lower repetition sets with higher loads (29) as well as a similar repetition and weight range to this study (34) found no impairment on cardiorespiratory adaptations. Thus, the lack of an aerobic adaptation in our current study is likely due to an insufficient training stimulus in the COMBINED group.
In terms of anaerobic fitness, both training programs resulted in increases in relative peak power output and relative average power output during a 30-second Wingate cycle test, although only the CIRCUIT group improved relative minimum power output. Similar increases in anaerobic power with circuit-based training and traditional resistance training have been previously demonstrated (11). The increases in leg strength in the COMBINED group (see below) likely played a role in the increase in anaerobic performance (1,32). While this was also a possibility in the CIRCUIT group, other metabolic adaptations (increases in glycolytic enzymes, improved muscle buffering capacity, and ionic regulation) resulting from training under constant fatigue likely factored in Ref. 31.
Both CIRCUIT (26,40) and COMBINED (2) groups increased muscle strength in the chest and hamstrings, although only the COMBINED group increased back and quadriceps strength. No change in strength for the back could perhaps be expected in the CIRCUIT group as they only used body mass–resisted exercise with no equipment, and therefore, no exercises targeted the back directly. This limitation of no specific back exercises in the CIRCUIT group and the increase in back strength in the COMBINED group highlights the necessity to target-specific muscle groups (i.e., with extra equipment) to train the back musculature. Further research should examine how to increase back strength in a whole-body aerobic style resistance training exercise routine with minimal equipment. The lack of change in quadriceps strength is surprising due to the heavy focus on squats and lunges. Perhaps the quadriceps need to be loaded with additional weight (greater than body mass alone) to generate increases in strength as they are a major load bearing and supporting muscle group during normal gait (3,35). However, the possibility of a type II error cannot be overlooked as CIRCUIT training did result in nonsignificant 8.3% increase in quadriceps strength. The similar increases in chest and hamstring strength between the CIRCUIT and COMBINED groups is impressive considering the COMBINED group trained using the pre- and post-testing exercises, therefore should have had greater test-specific learning, coordination, and neuromuscular recruitment (33). Moreover, the CIRCUIT group increases in muscular strength occurred along with the aforementioned increases in aerobic fitness, which is in contrast to the COMBINED group and previous research on concurrent training (4,19).
In this study, we used the participants current 60% 1RM weight to test muscular endurance, which resulted in both groups performing less repetitions posttraining. Although the COMBINED group lifted a significantly higher number of repetitions posttraining compared with the CIRCUIT group, they still had a reduced muscle endurance overall. Perhaps, test-specific learning, coordination, and neuromuscular recruitment may explain this improved muscle endurance posttraining compared with the CIRCUIT group but not pretraining data. This is in contrast to previous research using a whole-body aerobic resistance interval training program (Tabata protocol) in recreationally active females (27). The main difference could be due to the current use of 60% of their current 1RM, whereas McRae et al. used a specific percentage of body mass. Moreover, high-repetition low-weight training has also demonstrated significant increases in muscular endurance (9).
Our results are limited to the sedentary female population, and investigations into the effectiveness of aerobic whole-body resistance circuit training on measures of cardiorespiratory and muscle power are warranted in the male population. In an effort to limit our training to the specified time periods, the variety and modality of exercise was constrained along with the number of repetitions that could be performed. This limitation may have influenced the outcome, such as the regional increases in strength, but demonstrated that a time-constrained training program is effective. Considerations toward endurance measures relative to body weight or absolute muscular endurance could be addressed in the future.
A 5-week aerobic whole-body resistance circuit training of 30 minutes per session is sufficient for improvements in cardiorespiratory power, anaerobic power output, and muscle strength in sedentary females. Similar adaptations in anaerobic power output and muscle strength were observed in traditional concurrent resistance and endurance training of 45 minutes per session without the added benefits of increased cardiorespiratory power. Aerobic whole-body resistance circuit training is an effective time-efficient method of improving health determinants in sedentary females.
T. R. Myers and M. G. Schneider contributed equally.
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