Unilateral vs. Bilateral Exercises - Improving Sprint and Agility

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Appleby, Cormack & Newton (2019)

This paper initially defined the differences between unilateral and bilateral exercises. Examples of unilateral exercises are any that distributes the load unevenly to generate instability. It is also important to mention that unilateral and asymmetrical exercises differ based on stability and support. The step-up exercise used in this study is a true unilateral exercise as it has a single point of contact. Asymmetrical exercises such as split squats and lunges are performed with 2-points of contact where the focus is on one side. It was also suggested that the athlete could attain more neuromuscular adaptations from unilateral exercises than bilateral or asymmetrical.

The authors indicated that bilateral exercises are shown to improve strength and 5 to 40-m sprints. Sprinting and change of direction (COD) are predominantly single-leg movements. Therefore, it's presumed that unilateral exercises offer better adaptations than bilateral exercises.

The key exercises utilised in this paper are the bilateral back squat (BS) and the barbell step-up (SU). Although it appears that the SU presents more sport specificity, little research has been conducted regarding COD and sprints.

This paper aimed to discover any differences in COD and sprints depending on the specificity of the exercises (unilateral vs. bilateral). The authors hypothesised that unilateral exercises will be better for COD. The rationale is to provide an insight into whether movement specificity for lower-body exercises can improve athletic performance.

Method

• A randomised controlled design with a 6-week familiarisation period, an 8-week intervention and a 3-week maintenance.
• Three groups: Back Squat (BS), Step-Up (SU) and a control group (CON).
• BS and SU performed the same training, only differing in individual training loads and squat exercise.
• Subjects trained lower-body twice-a-week with either BS or SU - depending on group assignments.
• Thirty-three male rugby players completed the intervention.
• A minimum of 3 days of recovery between physical and testing sessions.
• Standardised 20-minute warm-up with lower-body mobility and countermovement jump.
• Subjects performed either the sprint or COD test before the maximal strength test for BS or SU. There was a 30-minute rest before the strength testing and participants were randomly assigned to either sprint or COD and BS or SU.
• Box-height for SU was measured and recorded to allow for accurate placement each visit.
• Lower-body 1-repetition max (1RM) was conducted for BS and SU.
• Subjects gradually increased the load to their 1RM for BS and SU. A no-repetition was given if the desired squat depth and extension were not achieved.
• Subjects were tested for 20-m sprints and COD.
• The COD test consisted of 2 gates and a target on the floor. The procedure was as follows:
  • Gate 1
  • 2.5-m sprint
  • Target
  • Change of direction (50 degrees)
  • 2.5-m sprint
  • Gate 2
• The subjects must land with the pivot foot within the target box before changing direction. Missing the box or stepping on it would result in a no-repetition.
• The COD test consisted of 3 trials on each leg and a 2-minute rest between each one.
• The sprint test consisted of a 20-m sprint starting in a self-selected starting posture.

Results

The BS and SU group both significantly improved 1RM. However, differences between groups were unclear, with a small difference in 1RM favouring SU. There was a meaningful difference in sprint acceleration between SU and BS, though the contrast is also unclear. BS showed moderate improvements for COD compared to SU.

These findings are interesting as it implies that exercise specificity may not provide the suspected adaptations. Although COD is predominantly an alternating unilateral movement, this study found that bilateral exercises improved COD moderately. The authors further implied that this could be due to the biomechanistic adaptations required to improve COD. For instance, a key variable of COD is the athlete's ability to capture the initial momentum and to apply an impulse in another direction. Other studies have shown that this challenges the athlete's ability to tolerate eccentric load, which is associated with the neuromuscular capacity for COD.

Relating this to the study, the SU is a concentric-dominant exercise compared to the BS. Therefore, this could indicate that the neuromuscular physiology of contraction type must be taken into account when designing an effective programme for improving athletic performance.

Practical applications

Maximal force developed from training with unilateral or bilateral exercises can be transferred into sprint acceleration. However, for COD, trainers must consider the underlying neuromuscular physiology of contraction types. They should not design a programme based on similarity in movements.

Limitations

The sample used in this study consisted of training athletes during pre-season. As it is a team sport, training variations and intensity could affect the adaptations experienced by each athlete.

Furthermore, there were difficulties in determining loads for BS and SU. It is a recognised issue in other studies and this could result in unequal training stimuli between groups.

References

Appleby, B., Cormack, S., and Newton, R. (2019). Unilateral and Bilateral Lower-Body Resistance Training Does not Transfer Equally to Sprint and Change of Direction Performance. Journal of Strength and Conditioning Research, 34(1), pp. 54-64.