Vaquera, A, Suárez-Iglesias, D, Guiu, X, Barroso, R, Thomas, G, and Renfree, A. Physiological responses to and athlete and coach perceptions of exertion during small-sided basketball games. J Strength Cond Res 32 (10): 2949–2953, 2018—This study describes heart rate (HR) responses during different small-sided games (SSGs) in junior basketball players and identifies the level of agreement between athlete and coach perceptions of internal training load calculated using the in-task rating of perceived exertion (RPE) method. Over a 6-week period, 12 male junior basketball players, who played in the Spanish national under-18 League, played 7 games of one-a-side (1v1), 6 games of 2-a-side (2v2), 8 games of 5-a-side (5v5), and 5 games of superiority (3v2) situations. During 1v1, 2v2, 5v5, and 3v2, peak HRs were 90.27±3.37%, 92.68±3.29%, 92.01±3.48%, and 88.74±5.77% of HRmax, respectively. These differences were statistically significant between 1v1 and 2v2 (p< 0.01), 1v1 and 5v5 (p≤ 0.05), 2v2 and 3v2 (p< 0.001), and 5v5 and 3v2 (p< 0.001). Mean HR was 79.5±4.4%, 83.1±4.2%, 91.2±4.7%, and 78.5±7.5% of HRmax during 1v1, 2v2, 5v5, and 3v2, respectively, and differences were observed between 1v1 and 2v2 (p< 0.001), 2v2 and 3v2 (p< 0.001), and 5v5 and 3v2 (p≤ 0.05). There were differences in athletes and coaches in-task RPE in all SSGs (all p< 0.0001 apart from 5× 5 p= 0.0019). The 2v2 format elicited a higher mean in-task RPE in comparison with all other SSGs (p< 0.001), possibly because 2v2 imposes a greater cognitive load.