Effects of unstable training on muscle activation: a systematic review and meta-analysis of electromyographic studies

To systematically evaluate the effects of unstable training (UT) on muscle activation and provide activation prescriptions for different muscle regions, offering more targeted guidance for different populations in muscle activation.

Data extraction and meta-analysis were conducted using RevManager 5.3, Stata 16.0, and R software. Subgroup analyses were performed on five variables: exercise equipment, exercise intensity, exercise mode, exercise experience, and contraction mode. Heterogeneity and publication bias were also examined.

A total of 28 studies were included, involving 579 participants. Comparison of activation effects between unstable training and stable training: Significant increases in core muscle activation, including rectus abdominis (SMD = 0.32, 95% CI [0.18-0.46], P < 0.01), internal oblique (SMD = 0.38, 95% CI [0.20-0.56], P < 0.01), external oblique (SMD = 0.38, 95% CI [0.20-0.56], P < 0.01), and erector spinae (SMD = 0.60, 95% CI [0.17-1.02], P < 0.01); Significant increases in upper limb muscle activation, including biceps brachii (SMD = 0.52, 95% CI [0.23-0.80], P < 0.01), trapezius (SMD = 0.23, 95% CI [0.12-0.35], P < 0.01), serratus anterior (SMD = 0.33, 95% CI [0.07-0.59], P = 0.01), and triceps brachii (SMD = 0.24, 95% CI [0.04-0.45], P = 0.02); Significant increases in lower limb muscle activation, including soleus (SMD = 0.65, 95% CI [0.42-0.87], P < 0.01), gluteus medius (SMD = 0.28, 95% CI [0.05-0.52], P = 0.02). In subgroup analysis, the core muscles with the great effect were: rectus abdominis (Bosu ball, body weight, sit-ups), internal oblique (Swiss ball, relative load, bench press), external oblique (Swiss ball, body weight, sit-ups), erector spinae (TRX suspension, body weight, bridging); the upper limb muscles with the great effect were: biceps brachii (more than 1 year of training experience, TRX suspension, body weight, muscle-up), trapezius (less training experience, Bosu ball, body weight, push-ups), triceps brachii (body weight). The lower limb muscles with the great effect were: soleus (squats). Negative activation effects: erector spinae (Swiss ball, 60% 1RM load, and shoulder press), serratus anterior (Swiss ball), triceps brachii (more than 1 year of training experience), Swiss ball, >60% 1RM; rectus femoris (Bosu ball, squats).

Unstable training is an excellent choice for rehabilitation after sports injuries, pre-exercise activation, and enhancing specific sports abilities. It can significantly activate core, upper limb, and lower limb muscles. In the future, more rigorous research should be carried out, providing a larger sample size and more meticulous evaluation methods for further comparative analysis.