Muscle endurance of the upper and lower extremity.

Rationale:

Muscle dysfunction is commonly observed in patients with chronic obstructive pulmonary disease (COPD). It is unclear whether the muscle dysfunction is generalized or if it mainly affects the lower extremities. At present, a wide range of test models and protocols is being used for quantification of muscle endurance in COPD patients. These can be divided on basis of muscle activation strategy, involving voluntary effort or exogenous stimulation. Since the main complaints in COPD are dyspnea and fatigue, it can be expected that COPD patients are not fully motivated to perform an endurance test. Consequently, tests involving maximal voluntary contractions (MVC’s) are likely to obtain sub-maximal test results when used in COPD patients. Limitations of voluntary manoeuvres are overcome by non-volitional muscle activation. Stimulation of motor endplates is effort-independent and seems feasible in quantifying arm and leg muscle endurance in COPD patients. Before using electrical stimulation extensively in a clinical population (such as COPD) to test muscle endurance in the lower and upper limbs, the reproducibility of the test needs to be examined in healthy subjects.



Objectives:

1. Examine the reproducibility of the non-volitional endurance test in healthy subjects. The hypothesis is that the non-volitional endurance test is reproducible;

2. Comparison of muscle endurance tested at three different stimulation intensities. It is hypothesised that there is no effect of stimulation intensity;

3. Comparing endurance between the arm and leg muscle in healthy subjects. It is expected that arm muscle endurance is lower than leg muscle endurance.



Study design:

Reproducibility study. The total duration of the experiment for the healthy subjects will be 225 minutes, divided over five visits. During the first visit, subjects will be asked to perform three maximal voluntary contractions with their biceps brachii and quadriceps femoris on a dynamometer. During the next four visits, the subjects will perform leg and arm endurance tests with use of muscle stimulation. These tests will be implemented on three different intensities and the last test will be repeated at the highest of the three intensities. The electrical stimuli (300s: 2s on 2s off, 30Hz) will be delivered trough two rubber electrodes on the motor end plates of the biceps brachii and of the quadriceps femoris.



Study population:

16 healthy subjects.



Main study parameters/endpoints:

Muscle endurance: TLIM (number of contractions until 20, 30 and 40% torque decline), steady state (% peak torque), transition point of the force decline curve (s) of the elbow flexors and knee extensors.

1. Examine the reproducibility of the non-volitional endurance test in healthy subjects. The hypothesis is that the non-volitional endurance test is reproducible;

2. Comparison of muscle endurance tested at three different stimulation intensities. It is hypothesised that there is no effect of stimulation intensity;

3. Comparing endurance between the arm and leg muscle in healthy subjects. It is expected that arm muscle endurance is lower than leg muscle endurance.

Endurance tests will take place on separate days, to prevent for muscle fatigue at the start of the endurance test. During the first visit, subjects will be familiarized with all equipment and testing procedures and perform a leg and arm maximal strength test. During the next three visits, the subjects will perform three leg and three arm endurance tests, on three different stimulation intensities.

Measurement of quadriceps and biceps muscle endurance using electrical muscle stimulation.