Progressive Resistance Training of the Extensor Muscle of the Thigh in COPD-patients Hospitalized With an Exacerbation

Background Chronic obstructive pulmonary disease (COPD) is one of the most costly chronic diseases (1). In Denmark it can be estimated that approximately 400.000 people suffers from COPD amounting to about 15% of the adult population. COPD causes 10.000 visits to the emergency room, approx. 25.000 acute admissions to hospital and 3.500 deaths a year. The disease costs approx 2 billion Danish croners (400 million dollars) a year. Hospital admissions due to exacerbations adds to the most costly part of the disease burden to society. COPD is one of the few chronic diseases still on the rise (1).

COPD is characterized by an accelerated decline in lung function. Most of the patients with severe degree of COPD suffer from recurrent acute deterioration named exacerbations. An exacerbation is defined as a deterioration in symptoms including shortness of breath and sputum production leading to a chance in medical treatment. Frequent exacerbations are associated with an extra high rate of decline in lung function and a strongly negative impact on the quality of life. The disease progression is followed by a gradual loss in muscle mass and strength (3).

Admission to hospital has well known effects on maximal oxygen consumption and a reduction in the physical condition leads to a more severe degree of shortness of breath during physical activity (4). Just a few days in bed is followed by an important loss of muscle mass and strength. Immobilization causes a decrease in metabolism and a loss of active motor units and a reduced ability to activate the resting motor units. This has a greater negative impact on the strength in the extensors that are engaged in maintaining the upright position than other muscle groups. In keeping with this, the loss of muscle strength occurs at twice as high a rate in muscles of the lower limb than in those of the upper limb (5). This leads to an increased production of lactic acid and corresponding muscle fatique (6). Muscles engaged in knee extension loose strength at the highest rate during immobilization. This loss has great impact on the activities of daily life such as getting out of bed, rising from a chair and climbing stairs. Even though the patients regain their premorbide lung function and their symptoms improve to the "normal" level usually within 6 weeks, they do not reach their habitual level of physical activity as expressed by the 6MWT (7). Admittance due to exacerbations is followed by muscle wasting and prolonged inactivity, leading to an increased risk of recurrent exacerbations.

Physical training of the muscles is the most efficient treatment to maintain or increase muscle strength to prevent muscle wasting during immobilization. Since most of the decline in muscle strength occurs during the first days of bed rest - 3-4% per day - and most pronounced in the muscles of the lower limb, there is god reason for early intervention with physical training of the extensors of the lower limb, the earlier after admittance, the better.

There is solid evidence for a positive effect of training of clinically stable COPD patients. Only two studies have investigated the effect of training during admittance for an acute exacerbation (8) In the study by Troosters, the training consisted of 3 sets of 8 repetitions amounting to 70% of 1 repetition maximum (1RM: repetitions maximum: the maximal weight that can be handled only one time). The subjects had an FEV1 of 40 ± 12 % of predicted, and were trained by the use of a knee extension machine. We do not know the exact exclusion criteria of the study - did they include patients who were unable to move from the bed to the knee extension machine? Did the physiotherapists handled the most severely diseased patients differently? Moreover, it would be more general applicable, if the training could be performed with a less demanding and expensive equipment than a knee extension machine. Accordingly, there is a need for at study with a more detailed description of the training procedure, using a simple, low cost training device, that is applicable to many centers and hospital units.