Energetics of landing: Effects of ankle instability

A diminished capability for energy dissipation at the knee after ground impact during landing in patients with chronic ankle instability may result in greater demands on the ankle joint. Modifying landing strategies could potentially reduce the risk of musculoskeletal injury.

By Masafumi Terada, MS, ATC, and Phillip A. Gribble, PhD, ATC, FNATA  

Participation in physical activity has an important role in a healthy lifestyle, but it is associated with an inherent risk of injury. Chronic ankle instability (CAI) is common after an initial acute lateral ankle sprain in physically active populations,^1-3 preventing patients from returning to their occupations^1,4 and leading to decreased health-related quality of life.^2,5 CAI is a condition characterized by self-reported disability, perceived instability (repeated episodes of “giving way”), recurrent ankle sprains, or all of these.^6,7

Potentially, CAI also may predispose an individual to the early onset of osteoarthritis,^8-10 which imposes a severe economic burden on the healthcare system worldwide.^11,12 Therefore, CAI is a significant public health concern in the physically active population. While research has examined various factors that may contribute to CAI, with the aim of minimizing the complications of CAI and maximizing the potential health benefits of a physically active lifestyle,^13-21 the mechanisms underlying the alterations associated with CAI are not fully understood.

Energy dissipation and CAI

Joint energetics have been suggested as biomechanical factors that contribute to lower extremity injury during a functional task.²² External forces and moments of force resulting from the foot’s impact with the ground during landing and the stance phase of gait can create a kinetic energy event. This can increase velocity at the hip, knee, and ankle joints in the sagittal plane, possibly leading to excessive unintended lower extremity joint motion. An internal force produced by eccentric extensor muscle actions contributes to the dissipation of the impact energy at each lower extremity joint.^23,24 It has been proposed that a greater ability to dissipate energy during functional tasks would be beneficial, as the lower extremity joints can provide adequate shock absorption while reducing stresses on the surrounding static joint stabilizers through their wide anatomical range of motion.^23,25,26 Thus, investigation of energy dissipation patterns during landing as part of a sports-related functional task may provide insight into the factors contributing to CAI.

In our recent work,²⁷ we observed altered energy dissipation patterns at the knee and ankle during a stop jump task in a CAI population. In participants with CAI the contribution to total energy dissipation was significantly greater at the ankle and less at the knee during the 100-ms interval following initial contact compared with healthy control participants (Figure 1). Therefore, our findings suggest the presence of CAI may alter the kinetic chain relationship throughout the lower extremity.

Individual joints of the lower extremity work together and influence each other during functional activities to provide dynamic joint stabilization throughout the kinetic chain. The demonstrated energy dissipation pattern at the ankle in our study may be an effort to increase landing stiffness and reduce stress on the static stabilizers in the unstable ankle by maximizing the contribution of the plantar flexors.

Suppressed gamma and alpha motoneuron activations and decreased corticospinal excitability in the muscles surrounding the ankle have been observed in individuals with CAI.^16,19,28 These inhibitions may make the muscle spindles less sensitive and lead to a decrease in muscle-tendon stiffness through lack of activation or tone in these muscles, resulting in an increase in electromechanical delay (EMD).²⁹ EMD is a measure of the time necessary for activation of a muscle to provide protective tension on its bony attachments and is an indirect indication of muscle stiffness and tone.^16,29

It has been reported that EMD of the fibularis longus muscle in individuals with CAI (23.6-33.7 ms) is longer than in those without CAI (19.5-19.8 ms).^16,30 The longer EMD associated with CAI may influence the energy dis­sipation pattern during functional tasks. An increase in EMD of the fibularis longus muscle may slow development of the muscle-tendon stiffness necessary for ankle joint protection.²⁹ To compensate for increased EMD and decreased muscle-tendon stiffness following ground impact, individuals with CAI may perform stiff landings at the ankle through a centrally mediated feed-forward compensatory mechanism. As landing stiffness increases, the relative contribution of the ankle plantar flexors increases while those of the knee and hip extensors decrease.^23,31

Investigators have described CAI as creating interplay between peripheral afferent nerves and a centrally mediated alteration in sensorimotor control, which is manifested in altered lower extremity movement patterns.^32,33 Therefore, it is possible the energy dissipation pattern de­m­on­strated by participants with CAI in our recent investigation may result from alterations in feedback and feed-forward neuromuscular control processes, which likely increases landing stiffness to compensate for an increase in EMD and a decrease in muscle-tendon stiffness and to protect the affected ankle joint^.27

Placing greater demands on the ankle joint to dissipate energy with limited ability to transfer force up the kinetic chain, however, could induce rapid fatigability during repetitive movements that may be related to development of CAI.

Potential knee injury implications

There is limited information to suggest a potential link between a history of ankle sprain and risk of knee injury.^34,35 Our recent data²⁷ on altered capability of kinetic energy dissipation at the knee joint, combined with previous findings of less knee flexion during a jump-landing task,^14,32,36 may provide insight regarding future knee joint injury mechanisms in individuals with CAI.

A more extended knee position, as well as decreased contributions from the knee to total energy dissipation, may contribute to an increase in knee injury risk. Previous authors have suggested that a decreased knee flexion angle during landing can lead to inadequate energy attenuation capability at the knee,^22,37 such that the knee joint experiences large compressive impact forces,²⁵ which in turn can lead to cartilage lesions and osteoarthritis³⁸ and increase the risk of anterior cruciate ligament (ACL) injury.²² Further, previous studies  have shown that restricted ankle dorsiflexion range of motion (DF-ROM) increases risk for patellar tendinopathy in young basketball athletes.^34,39 Backman et al³⁴ found a lower ankle DF-ROM in limbs with a history of  two or more ankle sprains compared with those with zero or one sprain as well as a trend of a higher incidence of patellar tendinopathy of limbs with two or more ankle sprains compared with those with zero or one ankle sprain.

These findings indicated that a history of ankle sprains may predispose for restricted ankle DF-ROM, potentially increasing risk for developing patellar tendinopathy. It has been observed that participants with restricted ankle DF-ROM have significantly decreased energy dissipation at the knee and increased energy dissipation at the ankle joint compared with those without restricted ankle DF-ROM.⁴⁰ Altered lower extremity landing biomechanics due to restricted ankle DF-ROM following an ankle sprain may increase load on the patellar tendon and risk for developing patellar tendinopathy.

In addition to diminished relative knee energy dissipation, increasing the demand on the plantar flexors to dissipate kinetic energy may be associated with an increased risk of future knee injury.^22,41 An energy dissipation strategy with greater contribution from the ankle plantar flexors may minimize the contribution of the proximal extensor muscles, putting the knee in a potentially injurious position.^22,41 Fleming et al⁴² have observed that greater gastrocnemius contraction results in significant increases in ACL strain when the knee is in a more extended position. Further, soleus muscle inhibition was previously documented in individuals with CAI.^28,43 This suggests the gastrocnemius muscle may be responsible for dissipating kinetic energy at the ankle in individuals with CAI. Research has also suggested²² that a landing pattern with greater ankle energy dissipation during the first 100 ms of landing may increase risk of ACL injury by resulting in greater gastrocnemius muscular force, which could contribute to increased ACL load. In our recent investigation²⁷ participants with CAI demonstrated a greater amount of energy dissipated at the ankle during the first 100 ms of landing compared with those without CAI, implying this energy dissipation pattern may have the potential for knee injury risk.

Modifying energy dissipation pattern

It has been accepted that the magnitude of energy dissipation can be controlled by adjusting the orientation of body segments relative to the ground reaction force (GRF) throughout a functional task.^23,24,26,44 Sagittal plane lower extremity joint motions during a dynamic task, specifically ankle dorsiflexion and knee flexion, play a significant role in attenuating the forces at impact.^23,45 The plantar flexors and knee extensors, which eccentrically control ankle dorsiflexion and knee flexion during landing, dissipate the majority of the kinetic energy.²³ Limited availability of ankle dorsiflexion reduces the ability of the knee extensors to decelerate the body’s center of mass (COM) and dissipate landing impact, which increases the demand on the ankle plantar flexors to dissipate energy, resulting in limited ability to transfer force up the kinetic chain.^46,47

Norcross et al²² reported a strong association between energy dissipation capability and sagittal plane kinematics at the knee and ankle joints. Decreased availability of ankle dorsiflexion has been observed in the CAI population.⁴⁸ Additionally, DeVita and Skelly²³ observed that landing with smaller knee flexion angles reduced dissipation of the kinetic energy by the knee musculature. It has been reported that participants with CAI demonstrated less knee flexion after initial contact during a jump-landing task than those without CAI.^14,36

With an extended knee at landing, the knee extensor muscles are in a less advantageous position to dissipate the experienced external loading after ground impact and store elastic energy.

The strength capability of the knee extensors is one of the critical elements of controlling energetic behaviors.⁴⁹ Deficits in force production by the knee extensors have been shown in individuals with CAI.¹³ Decreased force production by the knee extensors also leads to earlier activation of the ankle plantar flexors to provide compensatory dynamic knee stabilization by increasing joint stiffness.⁵⁰

Therefore, improving the availability of ankle dorsiflexion, increasing knee flexion during a jump-landing task, and improving knee extensor strength may be beneficial for maximizing the capacity for energy dissipation and should be considered as potential clinical interventions in patients with CAI.

However, sagittal plane kinematics at the knee and ankle are simply not enough to explain these relationships. Trunk flexion and stabilization of the body’s COM are also important contributors to energy attenuation capability.^24,32,51 Decreased trunk flexion may be a compensatory response to the reduced ability of the knee extensors to decelerate the body and attenuate landing impact.^52-54

Several authors have suggested the presence of CAI may influence the location of COM.^14,32,43 Improving jump-landing strategies, such as increasing trunk flexion and controlling the location of the COM before and during landing, may also be addressed in clinical interventions for patients with CAI. It will be beneficial for future investigations to determine whether such modifications in those with CAI could reduce both the CAI itself and the risk of future musculoskeletal injuries at the proximal joints.

Summary

The reorganization of the central nervous system with altered feedback responses following an ankle sprain may globally influence movement and muscle activation patterns during functional activities. Our recent work indicates the presence of CAI likely results in a landing strategy that shifts a greater demand for dissipating the kinetic energy of the landing impact to the ankle by increasing knee extension and use of the ankle plantar flexors.

Decreased knee extensor strength, coupled with altered knee kinematics and reduced ankle dorsiflexion availability, may lead to diminished capability for energy dissipation at the knee after ground impact during jump-landing tasks in CAI populations, which may result in greater demands on the ankle joint to attenuate external loading after ground impact. It will be important for clinicians and researchers to understand how the presence of CAI influences energy dissipation patterns in the entire lower extremity.

In the future, it also will be important to consider energetic behaviors associated with CAI that may be used to develop more effective interventions to target these potentially modifiable energy dissipation patterns. Continued work in this area is needed to determine whether the suggested modifications could reduce CAI, improve the level of function related to CAI, and minimize the risk for future knee injury.

Masafumi Terada, MS, AT, ATC, is a doctoral candidate in the Musculoskeletal Health and Movement Science Laboratory, Department of Kinesiology, at the University of Toledo in Ohio. Phillip A Gribble, PhD, ATC, FNATA, is professor of kinesiology, director of the Graduate Athletic Training Education Program, and codirector of the Musculoskeletal Health and Movement Science Laboratory at University of Toledo.

Disclosure: We certify that no party having a direct interest in the results of the research supporting this article has conferred or will confer a benefit on us or on any organization with which we are associated. No conflicts of interest are directly relevant to the content of this study.