Review 1: Ballor, D. Becque, M.D. and Katch, V. (1987)
Metabolic responses during hydraulic resistance training.
Medicine and Science in Sport and Exercise . 19 (4). 363-367.
Studies in circuit training in the early 1980's focussed on the metabolic responses to Universal and free weight resistance training movements in a variety of different formats. The majority demonstrated that when performed on a continuous basis, circuit training was effective in producing aerobic responses similar to many other large muscle aerobic activities. With the advent of hydraulic equipment and the introduction of the Super Circuit, where resistance exercises consisted of double concentric contractions, ensuring agonist and antagonist movements, anectdotally results appeared to be greater than the preceeding pin and free weight methods. By 1987 there had only been one study reported in the literature that had measured the responses to hydraulic circuit training (Katch at al, 1985). From this study the oxygen cost of the hydraulic circuit was reportedly 35% higher than studies that had measured Nautilus and Universal equipment.
The purpose of this study was to measure the oxygen cost (VO2) and heart rate response on 13 subjects who performed a 24 min 30 second circuit using a muti purpose hydraulic exercise machine.
Thirteen subjects were tested on maximal treadmill tests and were reported as being "highly fit". Subjects then performed seven different exercises (leg extension, bent over row, bicep curl, squat, upright row, bench press and behind the neck press). Each exercise was performed 3 times with the following work to rest ratio; 30 seconds exercise at a high speed setting, 30 seconds rest; 30 second exercise at a medium speed setting 30 second rest; 30 second exercise at a low speed setting 60 second rest. Each speed setting was changed according to changes in the orifice size of the hydraulic cyclinders. The exercise time was 90 seconds per station with a 120 second passive recovery for each station. During the recovery period there was no aerobic activity. During each exercise period, subjects were instructed to complete as many repetitions as possible. Open circuit spirometric technique was used to sample and analyze the expired gases.
On average the subjects exercised during the circuit at 41% of their treadmill VO2max and 81.2% of their treadmill heart rate max. computed to 68.7% of maximal heart rate reserve. The average oxygen cost of the circuit was 26.7 ml.O2. kg. min-1, while the corresponding heart rate was 153.83 beats. min-1. The oxygen cost within the exercise stations between high and low resistance settings was not different. In other words the resistance setting had little impact on the difference in intensity as related to the oxygen cost. This was probably due to the fact that more repetitions could be completed at the higher speed less resistance setting.
This in turn compensated for the increase in resistance of the lower speed greater resistance.
Application for the Personal Trainer
- When compared to other methods of circuit training such as Universal, Nautilus, and free weight, hydraulic resistance circuit training, whether expressed as a relative or absolute measure is reportedly aerobically higher. This may be due to the increased return of blood back to the heart apparently possible through double concentric exercises. In this study the subjects exercised at 41% of their maximal oxygen uptake. This was particulary impressive as the total time of actual exercise was 10 minutes of the total 24.5 minutes of the circuit and also allowing for the absence of aerobic stations in between. However, 41% of VO2m is marginally below the American College of Sports Medicine recommendations for an aerobic exercise training stimulus. In contrast, the heart rate reserve of 68.7% meets these recommendations. If however, the metabolic cost of each individual exercise is taken in account the stimulus is sufficient to meet this requirement. This is surely a strong case for the inclusion of aerobic interludes between each resistance station to increase the overall aerobic cost. In addition, when the overall energy expenditure of the circuit was calculated at 40.8 kJ.min-1 the ACSM recommendation for an aerobic stimulus was exceeded.
- The change in resitance settings from high speed to low speed showed little difference in the overall aerobic cost. It was reported that more repetitions were completed at the high speed than the low speed. Apparently, the increased resistance of the low speed was countered by the increased repetitions of the fast speed, at all times keeping the total work constant.
- The difference between heart rate response and aerobic cost of the reported circuit, places into the question the validity of using heart rate as measure of the aerobic intensity for exercise sessions conducted in this circuit fashion.