Effects of Co-Contraction Training on Neuromuscular Outcomes of Elbow Flexors and Extensors: A Systematic Review and Meta-Analysis

Abstract

Co-contraction training has been proposed to improve muscle strength in the absence of external equipment, yet it is needed to elucidate the effects of co-contraction training and its applicability. Thus, we synthesized the effects of co-contraction training on elbow muscle strength, myoelectric activity, and muscle thickness. We searched papers from MEDLINE via PubMed, Web of Science, Scopus and Embase databases. The inclusion criteria were studies comprising adults between 18-64 years old; investigating chronic effects of co-contraction training on elbow muscles; comparing pre- and post-intervention or control values; presenting any of the outcomes; randomized, quasi-experimental, pre- and post-design; in English. Seven studies met the inclusion criteria. We performed a systematic review and meta-analysis following PRISMA recommendations. We used the revised RoB 2, ROBINS-I to verify the level of evidence. We also included a questionnaire for biomechanical studies and GRADE analysis. We extracted data independently by two investigators, considering the characteristics of study, participants and training, outcomes, and results. We calculated the effect sizes for each outcome. The analysis was carried out by combining and dividing flexors and extensors in a subgroup analysis. Comparing the experimental vs. control group, our results showed that cocontraction training increased isometric strength (SMD=0.51 [0.19, 0.83]) and agonist myoelectric activity (SMD=0.54 [0.25, 0.83]). Comparing pre- vs. post-training, co-contraction training also improved isometric strength (SMD=1.28 [0.75, 1.81]); concentric elbow extensor strength (SMD=0.64 [0.01, 1.26]); and myoelectric activity (SMD=0.46 [0.18, 0.73]). No effect was observed for muscle thickness. The co-contraction training improves muscle performance without morphological changes.