Dehydration can impair aerobic performance, but its effects on muscular strength are still unclear. This study evaluated the effect of dehydration induced by cycling in the heat on exercised (knee extensors) and nonexercised (elbow flexors) muscles' strength and activation. Ten healthy recreationally active and nonacclimatized men (age, 22.71 ± 2.21 years old; body mass (BM), 77.94 ± 7.35 kg; height, 1.76 ± 6.46 m; body fat, 18.93 ± 3.01%) cycled in the heat in 2 separate sessions: dehydrated (DHY) and euhydrated (EUH). Dehydrated session led to a 2% BM loss, and water ingestion prevented the water loss in the euhydrated session. Knee extensor and elbow flexor maximal isometric torques and muscle activation were assessed before and after exercising in both sessions. Knee extensor torque decreased 15.8% (p < 0.001; 294.27 ± 44.82-247.16 ± 40.54) in dehydrated session, whereas no significant reduction (2.98%; p = 0.348; 291.99 ± 48.37-281.74 ± 38.65) was observed in the euhydrated session. No significant session-time interaction (p = 0.098) was observed for elbow flexor responses (DHY, 67.51 ± 14.53-62.95 ± 13.60; EUH, 68.26 ± 13.06-67.87 ± 13.89). Muscle activation capacity was unaffected by the hydration status. Maintenance of euhydration state during cycling in the heat may attenuate strength impairments caused by water loss in exercised muscle groups.