The main findings of the present study revealed that when a super-set method was initiated with the HQ order (leg curl + leg extension) an increased total training volume could be achieved with a lower RPE compared with the QH order (leg extension + leg curl). Considering this, the initial hypothesis is confirmed, since, in the leg curl preceding order, individuals presented a higher muscle performance.
It has been proposed that a preceding stimulation of the antagonist flexor muscle and its superior effect on the total training volume can be mediated by neural adjustment (Golgi tendon organ) allowing muscle actions to become more intense,21
or by an alteration on the triphasic neural pathway, suggested as a possible mechanism responsible for performance enhancement.6
Apart from this, Aagaard et al22
observed that antagonist hamstring movements counteract the anterior tibial shear and excessive internal tibial rotation induced by the contractile forces of the quadriceps near full knee extension. However, it has been shown that antagonist activation may not affect the performance of a standard isokinetic fatigue test.10
Thus, the decrease in the resultant joint moment after fatigue could be attributed to changes in agonist (knee extensor) muscle force-generation capacity rather than an altered moment of force exerted by the antagonist (hamstrings).23
Nevertheless, the exact neural mechanisms of flexor antagonist stimulation prior to knee extension remain to be elucidated in future studies.
The limitations of the present study are that no eletromyographic measures were made and the small, male-only, sample, which may limit the external validity of these findings.
An interesting feature of the present study is the use of conventional resistance training machines, since only a few studies using isokinetic devices investigated the effect of a super-set method involving the interchange between agonist and antagonist muscles of the lower limb.8
Although little has been reported on this phenomenon, it is known that exercise order can acutely affect muscle strength.12
Baker and Newton6
showed that muscle and power were increased by the previous use of the antagonist muscle for the upper body, highlighting the benefits of the super-set method for the upper body. However, when isokinetic equipment was used, the prefatigue of the antagonist muscle resulted in a reduced torque of the quadriceps at 60°.s-1, suggesting a limitation of the super-set method for the lower body.8
Alternatively, the results of the present study revealed that the super-set method was more effective for the total training volume by using the pre-activation of the hamstrings (leg curl) compared with the order that was initiated with the quadriceps (leg extension). The calculation of the effect size reinforced the above mentioned results with a moderate effect (between 0.50 and 1.50) favoring the HQ order. These results are different from those studies that used isokinetic machines, which are not commonly used in the daily practice of resistance training. In this sense, adding to the benefits of the super-set method on energy expenditure and time optimization in a resistance training session,5
this method can be effective in increasing total training volume when leg curl precedes leg extension. Kraemer and Ratamess24
indicated that total training volume is an important variable in muscle hypertrophy.
Another interesting result was that the RPE was lower in the leg curl + leg extension order. The use of the leg extension (quadriceps) first will exacerbate the RPE in a super-set method compared with the inversed order. It has been shown that the RPE can change with different resistance training volume.25
However, these explanations are rather speculative and require further investigation. The interchange between agonist and antagonist muscles possible when using a super-set method with conventional resistance training equipment is a promising area of research for investigators and resistance training professionals. Future studies using the super-set method should be carried out with acute and chronic designs and different exercise orders in different muscle groups and individuals, analyzing muscle hypertrophy, strength, and hormonal response, and with the use of electromyography.