The aim of this study was to assess lactate kinetics, maximal lactate accumulation rate (⩒Lamax) and peak power output (POmax) in a 15-s all-out exercise in handcycling (HC) and cycling (C) in terms of (1) reliability, (2) differences and (3) correlations between HC and C. Eighteen female and male competitive triathletes performed two trials (separated by one week) of a 15-s all-out sprint test in HC and C. Tests were performed in a recumbent racing handcycle and on the participants’ own road bike that were attached to an ergometer. Reliability was assessed using intraclass correlation coefficient (ICC). POmax and ⩒Lamax demonstrated high reliability in HC (ICC = 0.972, ICC = 0.828) and C (ICC = 0.937, ICC = 0.872). POmax (d = −2.54, P <0.0005) and ⩒Lamax (d = −1.62, P <0.0005) were lower in HC compared to C. POmax and ⩒Lamax correlated in HC (r = 0.729, P = 0.001) and C (r = 0.710, P = 0.001). There was no significant correlation between HC and C in POmax (r = 0.442, P = 0.066) and ⩒Lamax (r = 0.455, P = 0.058). Whereas the exchange velocity of lactate (k1) was similar in HC and C, the removal velocity (k2) was significantly higher in HC. ⩒Lamax and POmax during sprint exercise are highly reliable and demonstrate a correlation in both HC and C. However, since ⩒Lamax and POmax are significantly higher in C and not correlated between HC and C, ⩒Lamax and POmax seem to be extremity-specific.