FitCommerce: Unless one has been living in a cave, it's apparent that circuit training has made a revival lately as more deconditioned and/or overweight people are trying to find a way to ease into fitness with a small allocation of time. But circuit training is not really new, I believe I heard you say that circuit training dates back to 1953, is that correct?
Len Kravitz: You are so correct. Circuit training was developed by R.E. Morgan and G.T. Anderson in 1953 at the University of Leeds in England
Q: And, technically speaking, wasn't the Nautilus phenomenon of the 1980's, (and of course still around today) masked as a high-tech cam, really a just an advanced form of circuit training?
A: Absolutely. It is just a really effective means of training.
" … if you do not regularly change the stimulus to the muscle, all increases in strength or muscular endurance will plateau… "
Q: There may be many notions of what "circuit training" is, as an academic, can you define it for our readers? Does its results differ from free weights and other weight machines?
A: 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 program. Each participant moves from one station to the next with little (15 to 30 seconds) or no rest, performing a 15- to 45-second workout of 8 to 20 repetitions at each station (using a resistance of about 40% to 60% of one-repetition maximum). The program may be performed with exercise machines, hand-held weights, elastic resistance, calisthenics or any combination 
Q: Today, there has been an explosion of hydraulic training centers especially for women. Does it matter to the human musculature whether resistance is in the form of gravity, as with weights, or pressure against a piston?
A: Fabulous question. We study muscle physiology quite diligently at our university. In reality, a muscle cell (or group of muscle fibers) doesn't know if it is being trained with free weights, or by pressure or piston driven machines. Muscles cells essentially respond physiologically to LOAD and OVERLOAD by getting stronger via the process of increasing the size (and #) of protein filaments (and to NO LOAD by atrophying or protein filaments getting smaller). However, if the training is for sport performance or athletic achievement, the choice of exercise machines is important in as the overload that is more specific to the sport will have more skill cross-over benefits (in most cases).
Q: What about muscle memory and plateau. If a woman, religiously goes to her hydraulic gym 3 times a week for say, 9 months, doing exactly the same thing, will she still be progressing?
A: Another great question. Perhaps the most important message to share with students and trainers is the importance of "variety" of stimulus to muscle. Essentially, research has clearly shown that if you do not regularly change the stimulus to the muscle, all increases in strength or muscular endurance will plateau. Therefore, that is why it is much more advisable to use as many different exercises and types of exercise devices in the resistance training design to continually apply different stimuli to muscle.
" …it is much more advisable to use as many different exercises and types of exercise devices in the resistance training design to continually apply different stimuli to muscle… "
Q: Are there a minimum number of stations an exerciser should hit to get an appreciable amount of fitness?
A: I lend my answer to ACSM guidelines which recommend (minimally) 1 set of 8-10 repetitions for the major muscles groups of the body on 2 or 3 days of the week.
Q: Is there a particular order that one should follow in a circuit? That is, is there benefit to exercising certain muscle groups before others?
A: Typically, circuits have been designed with the multi-joint exercises (such as lunges, squats and bench presses) followed by the single-joint exercises (such as biceps curl and triceps extension). In addition, these designs often employ an upper body to lower body sequence so the consecutive exercises do not overly fatigue a specific body part or area.
Many great circuits also incorporate an agonist/antagonist (or opposite muscle approach such as doing the biceps curls and following it with triceps extension) methodology with the circuit design. I try to encourage professionals to design the circuits initially for the needs and goals of the client and to be careful about overloading a specific joint area too much (consecutively).
Q: With an increasing concern for osteoporosis mitigation in middle-aged women, in your opinion does hydraulic training offer sufficient overload to strengthen bones?
A: The key is not the exercise device but the overload used during the exercise. The overload needs to be sufficient enough to load bone. So, without a doubt, this is more specific to the program design and less a factor of the exercise device.
Females and males will definitely benefit from resistance exercise 3 times per week of both moderate- and high-intensities (up to about 70% of their maximum). However, there are always individual conditions to consider when working with special populations. People interested in starting a resistance-training program should consult with their physician first, especially if they are elderly, hypertensive, or have musculoskeletal injuries or diseases.
 Q: Can women really expect to add lean muscle mass by exercising for 30-minute segments with hydraulic machines, or are they just burning off calories?
A: Numerous investigations have been completed measuring the physiological benefits of circuit weight training. Circuit weight training has been shown to increase muscular strength from 7% to 32% while decreasing the percent of fat from 0.8% to 2.9%. The literature also shows an increase of fat-free weight (lean muscle) (1 to 3.2 kg) with no subsequent change in body weight. Kilocalorie expenditure has been estimated to be approximately 5 - 6 kcal per minute for women and 8 - 9 kcal per minute for men.
Q: As you peer into the short term future, would you care to guess what trends we may see in women's strength training?
A: I think your are on it with this circuit training piece. However, my crystal ball of fitness predicts many new and creative adaptations of this excellent training method. My advice to my fitness professionals is to be creative, use your knowledge of training, and design some exciting new circuit programs.
FitCommerce: Thank you for your insight, Dr. Kravitz.
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