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New Insights into Circuit Training
Len Kraviz, Ph.D.

Study Reviewed:
Gotshalk, L.A., Berger, R.A., and Kraemer, W.J. (2004). Cardiovascular responses to a high-volume continuous circuit resistance training protocol. Journal of Strength and Conditioning Research, 18(4), 760-764.

The new Dietary Guidelines for Americans provides science-based recommendations to reduce the risk for major chronic diseases and to promote health through diet and physical activity. Depending on a client’s 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 students. Fortunately, a newly published article on circuit training provides new research and training insights to help fulfill the modern challenges of exercise program design.

Circuit Training History and Fundamentals
Circuit training is an everlasting and evolving training exercise program 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 to 12 stations comprised the circuit. This number may vary according to the design of the circuit. Each participant moves from one station to the next with little (15 to 30 seconds) or no rest, performing a 15- to 45-second workbout of 8 to 20 repetitions at each station (using a resistance of about 40% to 60% of one-repetition maximum {1RM}). The program may be performed with exercise machines, hand-held weights, elastic resistance, calisthenics or any combination.

By adding a 30-second to 3-minute (or longer) aerobics station between each station, referred to 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 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 this study. All subjects were quite familiar with the correct performance and safety techniques of the exercises used in this study. Choosing pre-trained subjects allowed the researches a better opportunity to test, observe and analyze the physiological effects of the circuit training protocol.

Overview of Study Procedures
Strength and Cardiovascular Tests
Testing included strength and cardiovascular fitness assessments. Following standardized procedures, each subject performed a 1RM lift on the following 10 exercises: leg press, bench press, leg curl, latissimus pull-down, arm curl, seated press, triceps push-down, upright row, leg extension, and seated row.

On a separate day, subjects performed both submaximal and maximal aerobic capacity (or VO2max) treadmill tests which were 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/min. Heart rate and oxygen consumption were measured on the incremental (gradually increasing in speed and grade) maximal exercise test to exhaustion.

New Circuit Protocol Testing
A week after the strength and cardiovascular testing, subjects completed the circuit training protocol where oxygen uptake and heart rate were measured during 5 circuits of the 10-exercise protocol. Subjects performed 10 repetitions of each exercise at 40% of their measured 1RM. One major procedure insight from this study was the recommendation by one of the authors not to go higher then the 40% of 1RM (from unpublished data of the author). It should be noted that a goal of this program is to obtain a muscular fitness workout that also elicits a cardiovascular effect. Thus, it is important for fitness professionals replicating this 10-exercise study protocol with their clients not to be overly ambitious in increasing the load as this program has plenty of volume (reps x sets). Perhaps explaining to the client the goal of the program would be meaningful. All repetitions were performed at a 40 repetitions/min cadence and the only rest (2-5 seconds) was that needed to change exercises (exercises were performed on a Universal Gym multi-station device). A second major procedure insight from this study was the sequence and the methodology of the circuit order of exercises (See Table 1). The authors present and physiologically test a carefully planned order of the 10 exercises for the major muscles of the body. As seen in Table 1, the circuit sequence alternated joint actions two ways: 1) by performing opposite actions of a joint in series, and 2) alternating upper and lower-body joint actions. The objective of this sequencing was to provide an optimal rest period to the muscle groups involved in this workout program.

Physiological data was collected five times during the 5 circuits: after completion of 0.6 circuit (2:32 average minutes), 1.6 circuits (6:24 average minutes), 2.6 circuits (10:23 average time), 3.6 circuits (15:30 average minutes), and 4.6 circuits (16:36 average time). The subjects averaged 18.62 minutes to complete all 5 circuits.

The treadmill maximal test provides important maximal VO2 and HR data from which the physiological measures during the circuit performance can be evaluated. It is consequential to note that all subjects followed the same circuit sequence (Table 1), but started the circuit at different points. This scientific control helped to better substantiate the physiological results. Inspecting Figure 1, it is clear that the %maxium heart rate was much higher than the %maximum VO2 response.
Figure 1. Comparison of %VO2 Max and %HR Max Responses During Circuits

Although this study did not investigate physiological mechanisms 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 side as with 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 the actually oxygen consumption (and thus caloric expenditure) of a circuit training protocol.

Perhaps a 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% to 51.5% of VO2max) that meet established guidelines of the American College of Sports Medicine (ACSM) for the recommended intensity (40% to 85% of VO2maxR) of exercise for developing and maintaining cardiorespiratory fitness (Pollock et al, 1998). Thus, this circuit not only provides a suitable muscular fitness stimulus but also helps to meet ACSM cardiovascular guidelines and the newly published Dietary Guidelines for Americans 2005 for physical activity.

Bottom Line
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 evoke a satisfactory cardiorespiratory response. The study provides beneficial guidelines in circuit exercise choice, order, design and performance to improve or help to 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 participation. 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.

Additional References:
Kravitz, L. (1996). The fitness professional's complete guide to circuits and intervals. IDEA Today, 14(1), 32-43.

Pollock, M.L., Gaesser, G.A., Butcher, J.D., Despres, J-P, Dishman, R.K., Franklin, B.A., & Ewing Garber, C. (1998). The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Medicine & Science in Sports & Exercise, 30(6): 975-991.
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