Objective strength testing is indicated when a patient complains of strength deficits that you cannot detect on clinical examination, or for large muscle groups difficult to test using the MMT. Consequently, patients with large stature are natural candidates for strength assessment via dynamometry. Perhaps the most popular form of objective strength assessment is grip dynamometry. While grip dynamometry is relatively inexpensive, reliable, and easy to use, it cannot be used as a proxy measure of strength in patients with selective muscle weakness. This is certainly the case for patients with inclusion body myositis given the disproportionate involvement of their wrist flexors and knee extensors. Isokinetic dynamometry, while relatively expensive, offers superior stabilization during testing and provides a variety of testing modes. However, the time needed to conduct an isokinetic test precludes the testing of multiple muscle groups and it is difficult to position people with severe muscle weakness on the device.3
Handheld dynamometers provide more flexibility and less expense in comparison to isokinetic dynamometers. However, handheld dynamometers suffer from the same limitation as MMT: the outcome is dependent on the strength of the examiner. This type of device will exhibit high precision but low accuracy when used for large or strong muscle groups. The ideal objective strength-assessment device for both strong and weak patients is fixed dynamometry. Fixed dynamometers feature a plinth that allows for easy patient access and non-elastic straps attached to a frame to provide stabilization during testing (see Figure 1, below left). In our clinic, we record the clinical data from our dynamometry tests in absolute values, values scaled to body weight, and as a percentage of predicted force.
Progressive Resistance Training Paradox
The contributors to muscle weakness in adults with myositis include disease activity and damage, the effects of aging on muscle mass, and muscle atrophy secondary to inactivity. Exploratory clinical trials have shown that progressive resistance exercise is safe for people with acute and chronic myositis.1 Also, strength training has been successfully used to address the predictable decrease in muscle mass and power that is associated with sarcopenia. Successful exercise regimens depend on selecting the mode of treatment preferred by the patient and calculating the optimal exercise intensity. Multiple factors contribute to exercise intensity, but the most commonly cited element is load (i.e., the amount of weight lifted). Typical errors in the exercise prescription for strength training include using initial intensity levels that are too high or selecting low levels of intensity without a progression scheme.
