Metabolic and Structural Changes in Lower-Limb Skeletal Muscle Following Neuromuscular Electrical Stimulation: A Systematic Review

<div><p>Background</p><p>Transcutaneous neuromuscular electrical stimulation (NMES) can be applied as a complementary intervention to regular exercise training programs. A distinction can be made between high-frequency (HF) NMES and low-frequency (LF) NMES. In order to increase understanding of the mechanisms of functional improvements following NMES, the purpose of this study was to systematically review changes in enzyme activity, muscle fiber type composition and muscle fiber size in human lower-limb skeletal muscles following only NMES.</p><p>Methods</p><p>Trials were collected up to march 2012 and were identified by searching the Medline/PubMed, EMBASE, Cochrane Central Register of Controlled Trials, CINAHL and The Physical Therapy Evidence Database (PEDro) databases and reference lists. 18 trials were reviewed in detail: 8 trials studied changes in enzyme activities, 7 trials studied changes in muscle fiber type composition and 14 trials studied changes in muscle fiber size following NMES.</p><p>Results</p><p>The methodological quality generally was poor, and the heterogeneity in study design, study population, NMES features and outcome parameters prohibited the use of meta-analysis. Most of the LF-NMES studies reported significant increases in oxidative enzyme activity, while the results concerning changes in muscle fiber composition and muscle size were conflicting. HF-NMES significantly increased muscle size in 50% of the studies.</p><p>Conclusion</p><p>NMES seems to be a training modality resulting in changes in oxidative enzyme activity, skeletal muscle fiber type and skeletal muscle fiber size. However, considering the small sample sizes, the variance in study populations, the non-randomized controlled study designs, the variance in primary outcomes, and the large heterogeneity in NMES protocols, it is difficult to draw definitive conclusions about the effects of stimulation frequencies on muscular changes.</p></div

Enzyme activity following LF-NMES.

<p>Enzyme activity following LF-NMES.</p

Screening and selection process of trials.

<p>Screening and selection process of trials.</p

Effects of Body Mass Index on Task-Related Oxygen Uptake and Dyspnea during Activities of Daily Life in COPD

<div><h3>Background</h3><p>Patients with COPD use a higher proportion of their peak aerobic capacity during the performance of domestic activities of daily life (ADLs) compared to healthy peers, accompanied by a higher degree of task-related symptoms. To date, the influence of body mass index (BMI) on the task-related metabolic demands remains unknown in patients with COPD. Therefore, the aim of our study was to determine the effects of BMI on metabolic load during the performance of 5 consecutive domestic ADLs in patients with COPD.</p> <h3>Methodology</h3><p>Ninety-four COPD patients and 20 healhty peers performed 5 consecutive, self-paced domestic ADLs putting on socks, shoes and vest; folding 8 towels; putting away groceries; washing up 4 dishes, cups and saucers; and sweeping the floor for 4 min. Task-related oxygen uptake and ventilation were assessed using a mobile oxycon, while Borg scores were used to assess task-related dyspnea and fatigue.</p> <h3>Principal Findings</h3><p>1. Relative task-related oxygen uptake after the performance of domestic ADLs was increased in patients with COPD compared to healthy elderly, whereas absolute oxygen uptake is similar between groups; 2. Relative oxygen uptake and oxygen uptake per kilogram fat-free mass were comparable between BMI groups; and 3. Borg symptom scores for dyspnea en fatigue were comparable between BMI groups.</p> <h3>Conclusion</h3><p>Patients with COPD in different BMI groups perform self-paced domestic ADLs at the same relative metabolic load, accompanied by comparable Borg symptom scores for dyspnea and fatigue.</p> </div

Changes in muscle fiber size following NMES in healthy people.

<p>Changes in muscle fiber size following NMES in healthy people.</p

Enzyme activity following HF-NMES.

<p>Enzyme activity following HF-NMES.</p

Skeletal muscle fiber type composition following NMES.

<p>Data are shown as variation from baseline.</p

Borg symptom scores after performance of domestic ADLs.

<p>a. absolute Borg dyspnea scores. b. relative Borg dyspnea scores (%peak). c. absolute Borg fatigue scores. d. relative Borg fatigue scores (%peak).</p

Task-related oxygen uptake in patients with COPD and healthy controls.

<p>a. Absolute task-related oxygen uptake (mL/min). b. Relative task-related oxygen uptake (%peakVO₂).</p

Baseline characteristics by BMI categories.

<p>Results are presented as mean (standard deviation). FEV₁  =  forced expiratory volume in the first second; L  =  litre; FVC  =  forced vital capacity; kg  =  kilogram; kg/m²  =  kilogram per squared meters; Charlson CMI  =  Charlson co-morbidity index <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041078#pone.0041078-Charlson1" target="_blank">[19]</a>; Charlson CMI 2 =  Charlson age comorbidity index <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041078#pone.0041078-Charlson2" target="_blank">[20]</a>; 6MWD  =  six-minute walking distance; VO2 =  oxygen uptake; mL  =  millilitre; min  =  minute; BW  =  body weight; FFM  =  fat free mass; VE  =  minute ventilation; MVV  =  maximum voluntary ventilation; HR  =  heart rate; bpm  =  beats per minute. ^*1 kPa  = 7.5 mm Hg; ^**1 kilogram  = 2.2046 pounds; ^†p<0.05 vs. <21 kg/m² +p<0.05 vs. 21–25 kg/m²^#p<0.05 vs. 25–30 kg/m².</p