a mixture of experience, continuous learning and practical application.

MUSCLE FUNCTION Muscle function plays an important role in many rehabilitation-related issues. Knowledge of the various aspects of muscle function and its influence on athletic performance and injury is essential for all therapists who work in the sporting environment. Agonist and antagonistic muscle strength ratios can be used as rehabilitation goals for the injured athlete. In relation to the ankle joint, research has demonstrated a ratio of 25–28% dorsiflexion/plantarflexion (1) and 74% evertors/ invertors (2). However, opposing muscles do not work in the same mode of contraction during activity. A more meaningful approach physiologically is to use a ratio that compares the concentric performance of the agonist relative to the eccentric performance of the antagonist. This was initially examined at the knee (3), but more recently it has been utilised at the ankle joint (1). Increased co-contraction occurs around the ankle joint during jumping and sprinting. On foot contact, the ankle initially dorsiflexes concentrically with reciprocal lengthening of the plantarflexors (eccentric). The foot then moves into plantarflexion, concentrically with lengthening of the dorsiflexors under eccentric control. This provides more relevant information by evaluating eccentric muscle function and its potential to provide dynamic joint stability during fast forceful active movement. Muscle imbalance is commonly assumed to apply in relation to injury/re-injury. It is thought to occur if injury recovery is hindered by reduced muscle function. However, due to limited appropriate normative data, such a concept is difficult to accept as meaningful in relation to injury occurrence in most cases. The vast majority of research (4) indicates that the association of injury and muscle imbalance is a premature statement. More importantly, the type of muscle work, proprioception and electromyelographic (EMG) response is a better combination of factors to address. Many elite sportspeople use concentric/eccentric

pre-activation exercises in their warm-up drills before performance. Active movement involves the interaction of concentric/eccentric muscular activity with a far greater torque in high-speed sporting activity. Eccentric muscle action is needed both for athletic performance and in a protective role. It is selectively recruited during any change in momentum, either from the entire body or in an individual limb segment. It is essential to appreciate that the intramuscular force produced per motor unit is larger eccentrically than concentrically. The eccentric/concentric strength ratio for an individual muscle is normally 1.2–1.5. In relation to below-knee injury, the latter figure is the norm for ankle dorsiflexion due to its role in controlling load-bearing during gait (5). In many instances where the ratio is less than 1.2, the research subjects used produced low eccentric scores due to ankle injury pathology (6–8). This was due purely to ankle evertor weakness in these studies. As most ankle injuries occur with the heel elevated and all of the body weight on the forefoot, this is a logical statement. If, however, the heel is in contact with the surface and is weight-bearing, then the eccentric contraction of the ankle invertors may decelerate lateral displacement of the centre of gravity of the athlete. This would prevent movement of the heel and

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AGAINST AND ANTAGONIST MUSCLE STRENGTH RATIOS CAN BE UTILISED AS REHAB GOALS

rearfoot to its end of range limit, so reducing the demand on reciprocal concentric evertor contraction (9). Knowledge of the mode of injury is therefore essential in planning individual rehabilitation.

SPEED OF MOVEMENT Each joint in the human skeleton has to work at a specific angular velocity in order to produce a total movement pattern. Table 1 demonstrates the different speeds required at various joints during active exercise. This shows the wide spectrum of velocities required to go from walking to a specific high-speed activity. Following injury, the injured athlete is often reluctant to

work the injured area at the desired functional speed, which has a derogatory effect on gait pattern. Advantages of fast/ functional contractile velocity exercises include the following: n Re-education of functional activity n Decrease in joint compressive forces n Increase in synovial fluid lubrication with nourishment of the articular cartilage n Physiological overflow from faster- to slower-speed exercise. Performing rehabilitation programmes that include fast/ functional contractile velocity exercises therefore supports the principle of specific training for high-performance activity.

LINKAGE SYSTEM As discussed already, single joint/muscle factors, such as strength ratios, may be relevant only in isolated cases. In the multiple joint/muscle linkage system (16), physical deficits can affect whole-body performance in recreational and high- performance sporting activities. In the sporting environment, a muscle, muscle group or entire extremity needs to generate and absorb forces that may exceed its strength potential. From the opposite angle, injury to the foot and ankle interrupts the normal transmission of these muscular and joint forces along more proximal structures. When applied to physical therapy, the link system emphasises the interdependent nature of individual components and their ultimate contribution to the entire system. Recognition of this disruption to the knee, hip, pelvis, abdomen and upper limb is essential to ensure a complete rehabilitation programme.

TABLE 1: ANGULAR VELOCITIES AT VARIOUS JOINTS OF THE LOWER LIMB DURING ACTIVITY

Joint

Subtalar joint Ankle

Knee

Activity Running Running

Cross-country Skiing hill

Walking Running Karate

Velocity

540+/–167°/s 160°/s

268°/s

233°/s 1105°/s

1980+/–90°/s sportEX dynamics 2009;19(Jan):15-17 13–15

Reference 10

11,12