OBJECTIVE: To examine the evidence regarding functional electrical stimulation cycling's (FES-cycling's) physiological and clinical effects. DATA SOURCES: The study was conducted in accordance with the preferred reporting items for systematic reviews and meta-analyses protocol. PubMed, Embase, Cochrane Review, CINAHL, Scopus, Sport Discus, and Web of Science databases were used. STUDY SELECTION: Randomized controlled trials involving FES-cycling were included. Studies that did not involve FES-cycling in the intervention group or without the control group were excluded. Two reviewers screened titles and abstracts and then conducted a blinded full-text evaluation. A third reviewer resolved the discrepancies. DATA EXTRACTION: Meta-analysis was performed using inverse variance for continuous data, with effects measured using the mean difference and random effects analysis models. A 95% confidence interval was adopted. The significance level was set at P<
.05, and trends were declared at P=.05 to ≤.10. The I DATA SYNTHESIS: A total of 52 studies were included. Metabolic, cardiocirculatory, ventilatory, and peripheral muscle oxygen extraction variables presented statistical (P<
.05) and clinically important differences favoring FES-cycling, with moderate-to-high certainty of evidence. It also presented statistical (P<
.05) and clinically important improvements in cardiorespiratory fitness, leg and total body lean mass, power, physical fitness in intensive care (moderate-to-high certainty of evidence), and torque (low certainty of evidence). It presented a trend (P=.05 to ≤.10) of improvement in muscle volume, spasticity, and mobility (low-to-moderate certainty of evidence). It showed no difference (P>
.10) in 6-minute walking distance, muscle cross-sectional area, bone density, and length of intensive care unit stay (low-to-moderate certainty of evidence). CONCLUSIONS: FES-cycling exercise is a more intense stimulus modality than other comparative therapeutic modalities and presented clinically important improvement in several clinical outcomes.