Gotshalk, L.A., Berger, R.A., & Kraemer, W.J. 2004. Cardiovascular responses to a high-volume continuous circuit resistance training protocol. Journal of Strength and Conditioning Research, 18 (4), 760–64.
The new 2005 Dietary Guidelines for Americans (please see Food for Thought, page 80) provides science-based recommendations to reduce the risk for major chronic diseases and promote health through diet and physical activity. Depending on their clients’ needs and goals, fitness professionals are now faced with the challenge of designing anywhere from 30 minutes (to reduce the risk of chronic disease) to 60–90 minutes (for sustained weight loss) of daily physical activity for their clients. Fortunately, a recent scientific article on circuit training provides new research and training insights to help meet the modern challenges of exercise program design.
Circuit training is an enduring and evolving training exercise format that was developed by R.E. Morgan and G.T. Anderson in 1953 at the University of Leeds in England (Kravitz 1996). The term circuit refers to a number of carefully selected exercises arranged consecutively. In the original format, 9–12 stations comprised the circuit; this number may vary according to the circuit’s design. Each circuit training participant moves from one station to the next with little (15–30 seconds) or no rest, performing a 15- to 45-second work bout of 8–20 repetitions at each station (using a resistance of about 40%–60% of one-repetition maximum [1RM]). The circuit training workout program may be performed with exercise machines, hand-held weights, elastic resistance, calisthenics or any combination of these.
When a 30-second to 3-minute (or longer) aerobics station is added between stations, creating what’s known as aerobic circuit training, the method attempts to improve cardiorespiratory endurance as well (although this has not been conclusively supported in experimental research). This newly published article by Gotshalk and colleagues explores a circuit training workout protocol without the added aerobics stations to see if a cardiovascular effect can be attained.
Eleven college males who had completed a minimum of 11 weeks of a beginning resistance training program volunteered for the study. All subjects were quite familiar with the correct performance and safety techniques of the circuit training exercises. Choosing pretrained subjects allowed the researchers a better opportunity to test, observe and analyze the physiological effects of the circuit training protocol.
Strength and Cardiovascular Tests
Testing included strength and cardiovascular fitness assessments. Following standardized procedures, each subject performed a 1RM lift on each of the following 10 exercises: bench press, seated row, leg press, seated press, lat pull-down, upright row, leg extension, leg curl, triceps push-down and arm curl. Note: A sit-up was included in the circuit (making this an 11-exercise circuit), although no 1RM lifts were attained.
Two days later, subjects performed both submaximal and maximal aerobic-capacity treadmill tests separated by a 10-minute rest interval. For the submaximal cardiovascular test, oxygen consumption was monitored when treadmill running elicited a heart rate (HR) of 150 beats per minute. HR and oxygen consumption were measured on the incremental (gradually increasing in speed and grade) maximal exercise test to exhaustion.
One week after the strength and cardiovascular testing, subjects completed the circuit training protocol, during which oxygen uptake and HR were measured during 5 circuits of the 11-exercise protocol. Subjects performed 10 repetitions of each circuit training exercise at 40% of their measured 1RM (except the sit-up, which was performed on a 20% incline device). All repetitions were performed at a 40-repetition-per-minute cadence, and the only rests (2–5 seconds) were those needed to change exercises (exercises were performed on a Universal Gym multistation device).
One major procedure insight from this study was the recommendation by one of the authors not to exceed 40% of 1RM (from unpublished data of the author). A goal of this circuit training program was to obtain a muscular fitness workout that also elicited a cardiovascular effect. Thus, it is important for fitness professionals replicating this 11-exercise study protocol with their clients not to be overly ambitious in increasing the load, as this circuit training program has plenty of volume (repetitions × sets). Perhaps explaining the program’s goal to clients would be meaningful.
A second major procedure insight gained from the study was the sequence and methodology of the circuit order of exercises (see Table 1, below). The circuit was designed so that the sequence of lifts employed all major joint movements, with as much rest as possible given to each muscle group. Alternating joint action (e.g., when an exercise used shoulder flexion and elbow extension, the following exercise incorporated shoulder extension and elbow flexion) was used as much as possible, as was alternating upper- and lower-body action.
Physiological data were collected five times during the 5 circuits: after completion of 0.6 circuit (average time, 2:32 minutes), 1.6 circuits (average time, 6:25 minutes), 2.6 circuits (average time, 10:23 minutes), 3.6 circuits (average time, 15:30 minutes) and 4.6 circuits (average time, 16:36 minutes). The subjects averaged 18.62 minutes to complete all 5 circuits.
The treadmill maximal test provides important maximal VO2 and HR data from which physiological measures during the circuit performance can be evaluated. It is consequential to note that although subjects started the circuit at different points, all followed the same circuit sequence (Table 1). This scientific control helped to better substantiate the physiological results. Inspecting Figure 1, it is clear that the % maximum HR was much higher than the % maximum VO2 response.
Although this study did not investigate the physiological relationship of HR to VO2 responses to exercise, it should be noted that previous research has demonstrated that the use of arm variations (overhead, in front and to the sides, as in the exercises used in the circuit) often leads to a differential increase in exercise HR as compared to VO2. The important practical implication is that HR alone may be an inaccurate indicator of actual oxygen consumption (and, thus, caloric expenditure) during a circuit training protocol.
Perhaps the most profound finding of this study, from a health perspective, is that this investigation clearly shows that performance of this circuit of exercises, at this level of intensity, elicited oxygen consumption values (39%–51.5% of VO2max) that meet the exercise intensity guidelines (40%–85% of maximum oxygen uptake reserve [VO2R]) established by the American College of Sports Medicine (ACSM) for developing and maintaining cardiorespiratory fitness (Pollock et al. 1998). Thus, this circuit not only provides a suitable muscular-fitness stimulus but also helps meet ACSM cardiovascular guidelines and the physical activity component of the newly published 2005 Dietary Guidelines for Americans. However, since this circuit training exercise protocol elicits an intensity in the range of 40%–50% VO2R, it is more likely to result in fitness gains in those who are less trained, while helping to maintain fitness levels in moderately to highly trained individuals.
This evidence-based research demonstrates that when properly performed and sequenced, a continuous circuit training protocol at a low intensity (40% 1RM) and without aerobics stations can elicit a satisfactory cardiorespiratory response. The study provides beneficial guidelines in circuit training exercise choice, order, design and performance to improve or help maintain the muscular fitness and cardiorespiratory fitness for regular exercising students and clients. It should be noted that the subjects in this study had 11 weeks of resistance training experience before participating in the trial. Personal trainers and fitness professionals should always incorporate a safe and gradual progression with this and any exercise program. Notwithstanding, as fitness practitioners and personal trainers wanting to present the most effective exercise programs for our students and clients, it is somewhat reassuring to be able to use a circuit training program that has been scientifically authenticated.
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