Variability is a popular topic in sport. It is generally accepted that adding variability in practice can be advantageous to skill acquisition.
For instance, a golfer might practice a variety of shots from different distances. The same golfer might also explore different ways to swing the club to enable a draw or a slice.
With regards to the latter, the idea here is that the player will learn to perform the skill in a multitude of ways – a characteristic of skilled performers.
For coaches, this raises an important question: what is an effective strategy to induce variability in how skills are performed?
Johanna Brocken and colleagues devised a clever study that aimed to answer this question. Their study investigated the effect of practicing field hockey with a ball that rolled unpredictably (due to the ball having an asymmetric mass distribution).
129 girls aged 7 to 9 years with some experience playing hockey (ranging from 1 week to 4 years) participated in the study.
All participants engaged in 8 sessions of practice across 7 weeks. Half of the participants practiced with regular hockey balls for the first 4 sessions followed by modified hockey balls for the remaining 4 sessions. Conversely the other half of participants practiced in the opposite order. This experimental design is called a crossover design.
All participants performed a skills test at the start, after the 4th session, and at the end. The skills test demanded ball control and shooting skills, with performance measured as the time taken to complete the task.
The key finding is illustrated in the figure below. When practicing with the modified ball, children improved more in the skills test compared to when using the regular ball.
To explain the figure, Test 1, 2 and 3 on the x-axis refer to the timepoints when the skills test was performed (i.e., Test 1 = before the first session; Test 2 = after the 4th session; and Test 3 = after the final session). The 2 lines represent the 2 groups of participants, with the blue line representing the group who initially practiced with the modified ball. Importantly, a downward trending line reflects improvements in the skills test (i.e., reduced time to complete the task).
The group represented by the blue line improved their skills test performance significantly more than the other group (red line) in the first 4 weeks. However, this reversed in the final 4 weeks, which is when the group represented by the red line used the modified ball.
The authors articulated the reason for this effect as follows:
“… the more erratic rolling of the ball is thought to induce a more active exploration, creating a larger movement repertoire (i.e. degeneracy), which allows a learner to achieve the same task goal in different ways and to better adapt to different situations.”
The authors acknowledged, however, that they did not actually measure whether players were exploring a larger repertoire of movements. This remains a hypothesis.
An interesting finding in the study was that the players could not articulate what was different about the modified ball (other than that it was a different colour). This raises the possibility that the modified ball could induce a more implicit style of learning, whereby players learn to adapt their movements without being consciously aware of how they are doing it.
Extracted from Brocken et al. (2020)
Implications for Coaching
It is worth noting that movement variability is often induced in many sports due to the natural variation that exists in playing surfaces, such playing hockey on grass compared to synthetic fields, or playing cricket on softer pitches compared to hard pitches!
Brocken, J. E. A., van der Kamp, J., Lenoir, M., & Savelsbergh, G. J. P. (2020). Equipment modification can enhance skill learning in young field hockey players. International Journal of Sports Science & Coaching, 1747954120918964.