We have written often about the power of pulmonary rehabilitation in improving COPD patient physical conditioning, shortness of breath and quality of life. In most pulmonary rehabilitation studies, aerobic exercise (i.e. walking, cycling) is the primary exercise mode studied (although many studies also combine strength training with aerobic exercise).
So it was interesting to read a new study published in the journal Respiratory and Critical Care Medicine which showed 8 days of moderate strength training of the quadriceps muscles after an acute COPD exacerbation (doctor-speak for a shortness of breath attack significant enough to require hospital admission) improved muscular function and distance walked – even one month after discharge. (Troosters T, et al. Resistance Training Prevents Deterioration in Quadriceps Muscle Function During Acute Exacerbations of Chronic Obstructive Pulmonary Disease. Respiratory and Critical Care Medicine. May 2010: 181; 1072-1077)
Unlike pulmonary rehabilitation, which (when prescribed) is typically administered post-hospital discharge, this study sought to evaluate the effects of strength training during the 8-day exacerbation-related hospital stay of 36 COPD patients who completed the study. The research team divided the 36 patients into two groups. One group (17 patients) received quadriceps muscle strength training during their hospital stay while the other group (19 patients) received no training.
The group that trained the quadriceps muscles (the large set of muscles on the top of the leg between the hip and knee) performed 3 sets of 8 repetitions each day of their 8-day hospital stay on a knee extension weight machine (a machine which isolates the quadriceps muscles for strengthening). For this particular exercise, a person sits on the back supported seat of the machine, placing their feet behind a padded arm connected to the weights. The patient then raises their feet upward pressing their lower shins against the weighted arm of the machine until their toes reach approximately knee height. Then the patient lowers their feet and the weighted arm almost all the way back down before repeating this movement. The repetitions during the study were performed at an average of 70% of each patient’s 1-rep maximum force. Basically this means that at the outset of the study each patient was tested to see how much weight they could comfortably lift one time on the machine and then the researchers conducted the exercise sessions at approximately 70% of that weight.
Among other measures, the research team evaluated maximum quadriceps force and distance walked in 6 minutes for both the quadriceps training group and the control group which received no training. These measurements were taken at the beginning the study, at the end of the 8-day hospitalization, and again 30 days after discharge.
The results showed that the quadriceps training group produced an average 10% increase in quadriceps muscle force and distance walked in 6 minutes at the end of the 8 day hospitalization and more remarkably maintained both measures of improvement 30 days after discharge. By contrast, the control group saw their quadriceps muscle force and distance walked in 6 minutes decline slightly at discharge and decline slightly further 30 days after discharge.
For the quadriceps group, the research team viewed the degree of increase in quadriceps force as significant but did not view the improvement in distance walked as significant (typically in pulmonary rehab studies, an improvement of 50 meters walked in 6 minutes is considered clinically significant – the trained group in this study increased by only 38 meters).
Still, that’s pretty amazing improvement considering these COPD patients did not go through a formal 6-8 week pulmonary rehab program where they would have participated in both aerobic and strength training exercises for about an hour a day, 3 days a week over 6-8 weeks. They simply performed 3 sets of 8 reps of 1 exercise – knee extensions – each day of their 8 day hospitalization (which likely took less than 15 minutes to complete each day). This low level of activity over a very short period of time nearly achieved a clinically significant improvement in walking distance.
The research team theorized that encouraging physical activity as soon as feasible after a hospitalization for a breathing attack would help COPD patients recover from the exacerbation more quickly. In testing this hypothesis, they further believed that moderate strength training of a large, lower extremity muscle group like the quadriceps would place less intense breathing burden on a hospitalized COPD patient versus attempting aerobic exercise. Their results seem to bear out both suppositions as muscle strength improved and there were no adverse events reported by the group who underwent the exercise program.
Interestingly, the study team seemed a little surprised that the quadriceps force and 6 minute walk distance were maintained 30 days after discharge given the low dose/duration of the strength training regimen. They speculated that the quadriceps group patients may have become more active in basic daily activities post-discharge given that their quadriceps muscles had strengthened (i.e. the quadriceps muscles are the dominant muscles used when walking). It is another example of the power of even simple exercise to improve the fortunes of COPD patients.
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