Measuring Skeletal Muscle Strength and Endurance, from Bench to Bedside

Thierry Troosters, Katholieke Universiteit Leuven, Leuven, Belgium
Didier Saey, Institut Universitaire de Cardiologie et de Pneumologie,
Hôpital Laval, Québec, Canada

Skeletal muscle dysfunction is an important feature determining morbidity in many chronic diseases, including chronic obstructive pulmonary disease and congestive heart failure. Skeletal muscle weakness is a determinant of exercise intolerance,
excess utilization of healthcare recourses and mortality. Exercise training does
enhance skeletal muscle function and exercise performance. In addition, patients
who start a training program with impaired skeletal muscle function may be more
likely to respond adequately to an exercise training program. Hence assessment of peripheral muscle function is of interest to clinicians to identify more fragile patients
and to select patients for exercise training interventions. Researchers may get
insight in the mechanisms through which the disease (be it COPD or CHF) exerts
its systemic action, or may get further insight in the mechanisms of clinically
relevant improvements in physical activity levels, exercise capacity or health
related quality of life.

Measurement of skeletal muscle function range from a simple 5-point Medical
research scale or hand held dynamometry to utilization of magnetic stimulation
of peripheral nerves to elicit non-volitional contractions of the skeletal muscles.
The first techniques are ideally used bed-side. In the context of rehabilitation more standardized, machine based tests are more feasible and advisable. For research purposes, techniques which are independent of the voluntary muscle activation are
the golden standard. To gain complete insight in the skeletal muscle properties clinicians and scientists may be interested in muscle strength, endurance and fatigability. Recently it has become clear that skeletal muscle endurance may be
even more impaired than skeletal muscle strength. Several tests are used to measure skeletal muscle endurance. Most of these consist of repeated lifting of submaximal weights, or sustained isometric contractions. Skeletal muscle contractile fatigue
proved to be an important factor directly contributing to exercise intolerance. This skeletal muscle property, however, can only be addressed using rather complex research tools, involving magnetic stimulation. Symptoms of muscle fatigue, however, seem to be somewhat associated to contractile fatigue, and therefore may guide clinicians. Unfortunately there is no uniform guideline as to how to perform strength tests, endurance tests and tests to assess skeletal muscle fatigue. The present workshop, therefore will blend evidence base with expert opinion.

Recent insights in the importance of skeletal muscle function in chronic disease make this workshop timely. The aim is to review the different features of skeletal muscle function as well as a practical insight in the different techniques to assess skeletal muscle function. Clinical as well as research experience in dealing with these topics
will be exchanged, and recent literature giving insight in the usefulness of different
tests will be reviewed.