Functional ankle instability: jumping for joy?

New research suggests that the addition of plyometric training for ankle injury rehabilitation improves proprioception in athletes with functional ankle instability. Andrew Hamilton explains why introducing ballistic exercises into rehabilitation may improve functional outcomes.

Ankle sprains are among the most common musculoskeletal injuries in sportsmen and women. Up to 45% of sports injuries may be related to ankle instability, and 73% of individuals are likely to experience recurrent injuries^(1,2). When the structural stability of the lateral ligaments, such as the anterior talofibular ligament, is compromised, ankle instability becomes a risk (see figure 1). 

Figure 1: The lateral ligaments of the ankle.

The most common risk factor for lateral ligament ankle sprains is landing on an uneven surface⁽³⁾. A rapid and combined motion of plantar flexion and ankle inversion leads to excessive lateral movement. Proprioception is essential in neuromuscular control and affects ankle stability. Without sufficient proprioception, an athlete may be unable to react appropriately to the speed and magnitude of the perturbation.

The leading cause of chronic ankle instability is a previous injury. Following injury, there is an impairment in the mechanical properties of the lateral ligaments and joint capsule^(4-10).Combined with any deficits in proprioception, this results in a high re-injury rate and functional ankle instability (FAI). An FAI is defined as subjective ankle instability, giving way, and recurrent ankle sprains⁽¹¹⁾.

FAI management

An effective way of reducing ankle inversion injuries and improving proprioception is balance training⁽¹²⁾. Balance-training interventions of three and six weeks have demonstrated improved proprioception and postural stability. However, the effects of balance training on muscle activation in FAI are less clear. For example, individuals with FAI who undertook a period of proprioceptive training showed that the electrical activity (EMG) signals of the peroneus longus, brevis, and tibialis anterior showed no change during the first 60 milliseconds following a sudden external ankle inversion stimulus⁽¹³⁾. These findings provide clinicians with food for thought as optimal muscle recruitment is essential for minimizing the effects of unexpected perturbations.

Plyometrics and FAI

Athletes with ankle instability demonstrate an alteration of joint kinematics and neuromuscular control. Plyometrics exercises alter motor unit recruitment patterns and muscle activity by facilitating the sensorimotor system⁽¹⁴⁾. Increased excitability of the neurological receptors improves the reactivity of the neuromuscular system. Therefore, reducing the risk of injury by increasing the functional stability of the lower and upper limbs^(15,16).

The challenge for clinicians is that there is little evidence on the feasibility and effects of plyometric training for FAI. Combining plyometrics and balance may result in superior leg stiffness and running performance than plyometric training alone⁽¹⁷⁾. However, no investigations comparing plyometric training with and without added balance training in athletes with FAI exist. Thus, the use of plyometrics in FAI remains theoretical.

New research

Researchers at the National Cheng Kung University in Taiwan aimed to investigate the effect of integrated plyometric and balance training in participants with FAI during landing and standing positions⁽¹⁸⁾. Investigators randomized participants into three groups: plyometric training, integrated balance and plyometric training, or a control group that received no specific training. Each intervention lasted six weeks, and athletes trained two to three times per week. The content of plyometric training started with a simple squat jump and progressed to challenging jumps and hops. In contrast, the integrated training group involved jumps and a balanced squat or balanced lunge every week (see table 1)⁽¹⁸⁾.

The outcomes measured demonstrated that a six-week, isolated plyometric, and combined plyometric and balance training program improves ankle stability in sagittal and coronal planes at ground contact. Athlete’s static and dynamic postural control also improves with plyometric training. The significant improvement in inversion joint position sense for the integrated training group is consistent with current literature⁽¹⁹⁾. The researchers concluded that both balance and plyometric components should be selected based on the athlete's individual needs and incorporated into their training and rehabilitation. This strategy is likely to provide the very best outcomes in FAI.

Weeks	Plyometric Training	Repetitions	Session	Integrated: Plyometric-Plus-Balance Training	Repetitions or Time	Sets
1-2	Squat jumps	10	2	Squat jumps	10	2
	Ankle jumps	10	2	Balanced squat	10	2
	Jump for distance	10	2	Balanced dribble	20	5
	Forward zigzag jumps	10	3	Forward zigzag jumps	10	3
	Lateral sawtooth jumps	10	3	Lateral sawtooth jumps	10	3
	Jump up on step	8	2	Jump up on step	8	2
3-4	Split-squat jumps (right/left)	10	2	Split-squat jumps (right/left)	10	2
	Hop for distance (right/left)	10	2	Balance lunge (1 disc, right/left)	10	2
	Forward zigzag hops (right/left)	10	3	Forward zigzag hops (right/left)	10	3
	Lateral sawtooth hops (right/left)	10	3	Balanced single-leg standing (right/left)	10 seconds	5
	Tuck jump	10	2	Tuck jump	10	2
	Diagonal hop	8	2	Balanced catch ball	8	2
	Jump up on step	10	2	Jump up on step	10	2
5-6	Cycled single-leg squat jumps	10	2	Cycled single-legged squat jumps	10	2
	Hop on target (right/left)	12	2	Balance lunge (2 discs, right/left)	12	2
	Jump for distance and height	10	2	Jump for distance and high	10	2
	Forward zigzag hops (right/left)	10	3	Forward zigzag hops (right/left)	10	3
	Lateral sawtooth hops (right/left)	10	3	Balanced, single-legged standing dribble (right/left)	20	5
	Tuck jump	10	2	Tuck jump	10	2
	Agility ladder	3	1	Agility ladder	3	1
	Jump up on step	10	2	Jump up on step	10	2

Clinical implications

The positive clinical outcomes of plyometric training should provide clinicians with the necessary confidence and reasoning to include such activity in rehabilitation programs for FAI. Plyometric exercises are beneficial in improving the proprioception of individuals with ankle instability. Although isolated plyometric training led to a more rapid stabilization in ankle plantar flexion, integrated training programs provide a significant benefit.

Repetitive ballistic motions cause mechanoreceptors within or around targeted joints to undergo continual stimulation and improve the sensitivity of neuromuscular receptors⁽²⁰⁾. This explains why plyometric-trained athletes experience better functional outcomes. The integration of plyometrics into rehabilitation should be a key consideration for clinicians. Tissue healing should be respected when selecting rehabilitation exercises, but once appropriate, plyometric exercises provide a significant benefit in restoring ankle proprioception and may reduce the risk of re-injury.

References

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