How does elastic-resistance training affect performance?
It is important to note that this article will discuss using elastic bands for resistance purposes and not assistance, unless otherwise stated. For the purpose of discussion, and because a majority of the research has been conducted on it, the back squat with resistive elastic bands will be the example exercise used in this article.
Eccentric-Concentric Transition (SSC)
During this transition phase, or stretch-shortening cycle (SSC), as elastic-resistance increases muscle activity (5, 6) and rate of loading during the eccentric phase (6), it is often believed that there will be an increase in the storage of elastic energy and thus improvement in the following concentric performance (1). In other words, the assistance of the elastic bands during the descent is thought to load the eccentric-concentric SSC to a greater extent than free-weights alone, and thus improve the following concentric portion of the lift. As a result, it is somewhat rational to assume there may be an increase in the concentric rate of force development (RFD), however, this does not align with the research which suggests that ERT does not improve concentric RFD (4, 7).
Having said that, one very important aspect to consider is that both of these authors only measured average RFD, and not peak or any time-interval RFD. As elastic bands slow down the later stages of the concentric movement, using an average RFD may mask any improvements in early-stage RFD (i.e. the RFD at the beginning of the concentric phase). Therefore, ERT may not improve average RFD, but they may improve early-stage RFD, though no research has yet validated this. In support of this, Wallace et al., (4) reported an increase in peak power as a result of using ERT – though they did not identify at which part of the concentric phase they achieved peak power (e.g. early-, mid-, or late-stage).
Many strength and conditioning coaches often use ERT to overcome the weakest part of the exercise, otherwise known as the “sticking point”. It is this segment of any exercise that the joint levers are at their weakest position, this, in turn, determines the maximal weight an athlete can lift (3).
Continuing from the former point, it is thought that using elastic bands will either improve early-stage RFD and/or alter the mechanical disadvantage of the sticking point (1), therefore improving an athlete’s ability to overcome it. The first of these two reasons (i.e. early-stage RFD) has already been discussed. In order for them to reduce the mechanical disadvantage of the sticking point, the elastic bands must be used as an ‘assistive’ force as opposed to a ‘resistive’ one.
This means using the bands to make the concentric part of the lift easier, not harder, by simply placing them above the barbell instead of below. In this instance, it is believed that the bands offer a degree of unloading and may assist the acceleration of the barbell – helping the athlete overcome the sticking point (8). Though this is often a common thought, to the best of our knowledge, no scientific evidence supports this theory.
To further support this, as long-term ERT has been shown to improve maximal strength, then it may be suggested that they facilitate maximal strengths gains, and resultantly help overcome the sticking point (1).
End Range of Movement
The length-load profile of elastic bands means that with an increase in the stretch-length, there is an increase in the tension of the band to resist that stretch (Figure 2). In other words, the more the band is stretched, the higher its resistance to stretch becomes. Because of this, coaches often use elastic bands to increase an athlete’s strength at the end range of the movement (i.e. the top portion of the exercise), as this is where the bands provide the largest resistance.