The ankle poses problems not shared by the knee joint. As it is such a polyarticulating area with a wide variety of movements and masses of muscles spanning it, the ankle throws up many procedural issues, like positioning and alignment, and issues related to closed versus open chain testing.

Test ROM

Normal ROM of dorsiflexion is said to be 25 degrees while for plantarflexion it is thought to be 45-50 degrees (Miller, 1985) Figures range for both movements to ridiculous values, however, most people agree on one thing. The neutral position is equal to 0 degrees. To give you an idea of the functional ROM during walking there is approximately 10 degrees dorsiflexion to 20 degrees plantarlexion (Mcpoil and Knecht, 1985) whilst during running there is approximately 20 degrees dorsiflexion to 25 degrees plantarflexion (Soutas-Little et al., 1987). On this basis ROM over 45 degrees should really be avoided unless academic interest lies in this area.

The angle of peak moment has been found by Sjostrom et al. (1978) and Gerdle et al. (1988) to be somewhere around 25 degrees of plantarflexion (so make sure you include this in your test and look at the angle of peak torque).

Positioning

A modified seated position with the knee flexed to 90 degrees seems to be the position of choice (Backman and Oberg, 1989). 

 

Prone lying is another popular position and it has been shown that testing with full knee extension (avoid any flexion or hyperextension) yields results 10-15% higher than those in sitting. This is due in part to the assistance of the hamstrings to the gastrocnemius muscle. Be careful to ensure the knee is fully supported on the chair otherwise pain can occur due to hyperextension.

Testing can be performed for (plantar flexion only) in the more functional position of standing (see below). This offers an excellent ROM and good stability but is harder to position in the first instance.

Stabilization

The foot, shank and thigh must all be stabilized which is achieved easily on modern systems.

Alignment of IAOR

This is very simple. As described by Inman (1976) it is considered to pass through the malleoli (technically this forms an angle with the longitudinal axis of the tibia. Remember the tibia has an offset angle of 10 degrees).

In our example the lateral malleoli can be seen as the filled star aligning with the center of the actuator axis shown in the unfilled star.

Test Velocities

As the ankle is subject to velocities in the region of 150-200 degrees/second whilst walking there has been a propensity to use high speeds whilst testing (Sutherland et al, 1980). Velocities higher than 30 degrees/second are not usually required. Peak moment does tend to decline with increasing velocity. The moment at 120 degrees/second will generally be half that at 60 degrees/second. There does, however, appear to be a relationship between mean power and a test velocity of 180 degrees/second as described by Gerdle and Fugl-Meyer (1985).

 

Test ROM

Inversion and eversion takes place at the subtalar joint. Large individual variations exist in the amount of movement. The ROM should be between 30-50 degrees inversion and 15-20 degrees eversion (Miller, 1995).

Positioning and Stabilization

Most tests are performed in what is known as the loose packed position (that is the knee is flexed).

Testing in the close packed (with the knee straight) position eliminates the influence of the hamstring muscles on tibial torsion. However, this is difficult to replicate but should be used for research.

The amount of ankle plantar/dorsiflexion at the ankle should be considered, an optimum position of 0 degrees should be used (currently no one can agree on the influence of plantar and dorsriflexion on in/eversion strength).

Alignment of IAOR

Debate rages over the inclination required at the dynamometer head (i.e. how much it is tilted). Lentell et al. (1988) recommended this be set at 55 degrees.

Test Velocities

Medium test velocities of approximately 90 degrees/second are probably most useful, however, any speed from 30-240 degrees/second could be considered representative of the speed of subtalar movement during walking/running.

Interpretation:

Peak torque: If available compare to the opposite side.

          If you have tested both sides you should look to see if the sides are within 10 percent of each other (this is a good balance).

Concentric/concentric:

Inversion/eversion ratio should show a invertor dominance of 30 percent.

Plantar/dorsiflexion. A plantar flexor dominance of 70 percent should be expected over the dorsi flexors.

Concentric/eccentric:

For the concentric/eccentric results you should expect the eccentric value to be 30 percent higher than the concentric figure.

Normative values:

Unfortunately the establishment of normal muscle strength values at the ankle joint is not yet complete. A data base this large would require enough subjects who share a number of similar traits (gender, age, activity level, fibre types, health status, anthropometric factors). The same protocols would have to be used for each subject (contraction type, velocity, testing procedures, measurement device, peak moment, average moment etc.). Given the amount of variables it would seem impossible to provide a dependable normative framework. Yet, here  we have some.

Dorsiflexor concentric strength (subjects tested supine with full knee extension)

Female

Male

Dorsiflexors
30/sec	26	33
60/sec	20	26
120/sec	15	18
180/sec	12	12

Plantarflexor concentric strength (subjects tested supine with full knee extension)

Female

Male

	Sedentary	Trained	Sedentary	Trained
Plantarflexion
30/sec	84	140	126	183
60/sec	64	113	96	145
120/sec	39	75	60	95
180/sec	27	52	41	64

Invertor / Evertor concentric strength

Female

Male

Age	19-30	30-40	40-50	50-62	19-30	30-40	40-50	50-62
Invertors
60/sec	23	25	18	20	36	31	29	30
120/sec	20	21	18	17	32	26	25	23
Evertors
60/sec	20	18	20	16	29	25	25	24
120/sec	16	14	13	13	23	19	18	18