Hoff, J. Tjknnat, A. Steinshamn, S, Hkydal, M., Richardson, R. Helgerud, J.
In a disease that impacts O2 transport, such as chronic obstructive pulmonary disease (COPD), a diminished mechanical efficiency (work/oxygen consumed) would beexpected to worse the impact of this illness. There is growing evidence that a reduced mechanical efficiency often accompanies COPD. Initial evidence suggested that the increased cost of breathing associated with COPD might account for this mechanical inefficiency. However, in the wake of the recent interest in skeletal muscle changes associated with COPD, several studies have directly studied isolated locomotor muscle and have revealed reduced mechanical efficiency in these patients, which clearly is not a consequence of an increased cost of breathing.
The use of maximal strength training (MST) with an emphasis on the maximal rate of force mobilization in the concentric phase, consisting of high loads and few repetitions, has been reported to improve work economy by approximately 5–20%, even in subjects who were already exercise trained. Such potential improvements are certainly relevant to patients with COPD, who may experience both reduced O2 transport and reduced mechanical efficiency during exercise. Consequently, this study was designed to investigate whether MST can enhance mechanical efficiency during exercise in patients with COPD while also improving lung function via improvements in respiratory muscle function.
Twelve patients with COPD were pretested and then randomly assigned to either an MST group (n= 6) or a normal activity control group (n= 6). Within each MST training session (three times per week for 8 wk), patientsperformed four sets of seated leg presses with a focus on the rate of forcedevelopment at an intensity that only allowed the performance of five repetitions.
Patients who performed MST significantly improved 1 repetition max (1-RM) on average 27%, rate of force development by 105%, mechanical efficiency by 32%, and forced expiratory volume in 1 sec (FEV1) by 22 %, whereas these variables were unchanged in the controls. Neither group changed either maximal oxygen consumption or body mass.
Conclusion: The current findings reveal that because MST is minimally taxing to the ventilatory and cardiac systems, it is well suited to patients with COPD, not resulting in the normal dyspnea-associated discomfort experienced by this population during conventional exercise such as walking. This is highlighted in the current patients by the 100% compliance and completion of training in the MST group. The inclusion of MST in a cardiopulmonary rehabilitation program could result in more than30% improved mechanical efficiency. In the real world, this translates to either having the potential to perform significantly more work or to perform the same work with a reduced effort.
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