Study design: A systematic review. Objective: The aim of this review was to determine the effectiveness of physiotherapy (PT) interventions for increasing voluntary muscle strength in people with spinal cord injuries (SCI). Methods: We included randomised controlled trials of PT interventions for people with SCI. We were interested in two comparisons: PT interventions compared with sham or no intervention, and PT interventions compared to each other. The outcome of interest was voluntary strength of muscles directly affected by SCI. All included studies were rated according to the Cochrane Risk of Bias Tool and results of similar trials were pooled using meta-analyses where possible. Results: Twenty-six trials met the inclusion criteria and provided useable data. A statistically significant between-group difference was found in four comparisons, namely, resistance training versus no intervention (standardised mean difference (SMD) = 0.64; 95% CI, 0.22–1.07; p = 0.003); resistance training combined with electrical stimulation versus no intervention (mean difference (MD) = 14 Nm; 95% CI, 1–27; p = 0.03); a package of PT interventions versus no intervention (MD = 4.8/50 points on the Lower Extremity Motor Score (LEMS); 95% CI 1.9–7.7; p = 0.01); and robotic gait training versus overground gait training (MD = 3.1/50 points on the LEMS; 95% CI, 1.3–5.0; p = 0.0008). Conclusion: There is evidence that a small number of PT interventions increase voluntary strength in muscles directly affected by SCI.