Author(s): SEILER-VIKEN, S., LOSNEGARD, T., Institution: NORWEGIAN SCHOOL OF SPORTS SCIENCES, Country: NORWAY, Abstract-ID: 2144

INTRODUCTION:
“Double threshold” training has become a popular topic in running [1-3], yet few studies have experimentally investigated this training methodology [4]. We therefore compared acute physiological and perceptual stress responses between single and double daily moderate-intensity interval sessions during two short training blocks in well-trained runners.
METHODS:
Using a counterbalanced, repeated-measures, cross-over design, well-trained male (n=12, V̇O₂peak: 63.5±5.6 ml·kg-1·min-1) and female (n=13, V̇O₂peak: 56.7±3.9 ml·kg-1·min-1) distance runners completed two 11-day training blocks of single (Single) and double (Double) daily threshold interval sessions, including a 5-min all-out time trial (TT) on day 1 (Pre-test) and day 11 (Post-test). Each block included two Long interval sessions (Single: 6x6 min; Double: 2x(4x6 min), 60 s recovery) and two Short interval sessions (Single: 20x90 s; Double: 2x(12x90 s), 45 s recovery). Participants rested 5-7 h between Double sessions and had a 2-3 week wash-out between blocks. Running pace was matched between conditions and prescribed relative to the second lactate turn point (LT2): 0.5-1.0 km·h-1 below LT2 for Long intervals and 0.5-1.0 km·h-1 above LT2 for Short intervals. Each of the six test/interval days was separated by a standardized low-intensity training day (< 70% of maximal heart rate [HR]). TT measures included 5-min distance, peak oxygen uptake, peak HR, peak breathing rate (BR), peak blood lactate concentration, and peak rating of perceived exertion (RPE). Interval-session measures were HR, BR, and RPE. Before each session, participants reported readiness to train, muscle soreness, and perceived recovery score (PRS) using a 1-10 visual analogue scale. Linear mixed-effects models assessed differences between Single and Double sessions and Pre-test to Post-test performance measures. Significance was set at p < 0.05. Results are reported as estimates and Hedges’ g.
RESULTS:
The following session outcomes were significantly lower in Double than Single: HR (-2.38 bpm, g = -0.78), Interval RPE (-0.29, g = -0.59), Session RPE (-0.31, g = -0.54), Readiness to train (-0.29, g = -0.31), and PRS (-0.33, g = -0.37). No differences were observed in BR or muscle soreness. Performance outcomes did not differ between conditions, and no condition x time interaction was observed.
CONCLUSION:
Short-term double threshold training reduced acute internal stress responses and modestly increased perceived recovery cost relative to single daily sessions, without affecting performance ability from pre- to post-training blocks.
[1] Casado et al., Int J Environ Res Public Health, 2023
[2] Culp, 80/20 Publishing, 2024
[3] Tjelta, Int J Sports Sci Coach, 2019
[4] Talsnes et al., Front Physiol, 2024