Determinants of last lap speed in paced and maximal 1500-m time trials

The present study identified the physiological and performance characteristics that are deterministic during a maximal 1500-m time trial and in paced 1500-m time trials, with an all-out last lap.

Thirty-two trained middle-distance runners (n = 21 male, VO_2peak: 72.1 ± 3.2; n = 11, female, VO_2peak: 61.2 ± 3.7 mL kg^-1 min^-1) completed a 1500-m time trial in the fastest time possible (1500_FAST) as well as a 1500_MOD and 1500_SLOW trial whereby mean speed was reduced during the 0-1100 m by 5% and 10%, respectively. Anaerobic speed reserve (ASR), running economy (RE), the velocity corresponding with VO_2peak (_VVO_2peak), maximal sprint speed (MSS) and maximal accumulated oxygen deficit (MAOD) were determined during additional testing. Carnosine content was quantified by proton magnetic resonance spectroscopy in the gastrocnemius and expressed as a Z-score to estimate muscle fibre typology.

1500_FAST time was best explained by RE and _VVO_2peak in female runners (adjusted r² = 0.80, P < 0.001), in addition to the 0-1100-m speed relative to _VVO_2peak in male runners (adjusted r² = 0.72, P < 0.001). Runners with a higher gastrocnemius carnosine Z-score (i.e., higher estimated percentage of type II fibres) and greater MAOD, reduced their last lap time to a greater extent in the paced 1500-m trials. Neither ASR nor MSS was associated with last lap time in the paced trials.

These findings suggest that _VVO_{2 peak} and RE are key determinants of 1500-m running performance with a sustained pace from the start, while a higher carnosine Z-score and MAOD are more important for last lap speed in tactical 1500-m races.