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. 2024 Aug;124(8):2427-2438.
doi: 10.1007/s00421-024-05459-6. Epub 2024 Mar 28.

Durability of the moderate-to-heavy-intensity transition is related to the effects of prolonged exercise on severe-intensity performance

Kate Hamilton  1 , Andrew E Kilding  1 , Daniel J Plews  1 , Mathew J Mildenhall  2 , Mark Waldron  3   4 , Thanchanok Charoensap  1 , Tobias H Cox  1 , Matthew J Brick  1   5 , Warren B Leigh  1   5 , Ed Maunder  6
Affiliations

Durability of the moderate-to-heavy-intensity transition is related to the effects of prolonged exercise on severe-intensity performance

Kate Hamilton et al. Eur J Appl Physiol. 2024 Aug.

Abstract

Purpose: Power output at the moderate-to-heavy-intensity transition decreases during prolonged exercise, and resilience to this has been termed 'durability'. The purpose of this study was to assess the relationship between durability and the effect of prolonged exercise on severe-intensity performance, and explore intramuscular correlates of durability.

Methods: On separate days, 13 well-trained cyclists and triathletes (V̇O2peak, 57.3 ± 4.8 mL kg-1 min-1; training volume, 12 ± 2.1 h week-1) undertook an incremental test and 5-min time trial (TT) to determine power output at the first ventilatory threshold (VT1) and severe-intensity performance, with and without 150-min of prior moderate-intensity cycling. A single resting vastus lateralis microbiopsy was obtained.

Results: Prolonged exercise reduced power output at VT1 (211 ± 40 vs. 198 ± 39 W, ∆ -13 ± 16 W, ∆ -6 ± 7%, P = 0.013) and 5-min TT performance (333 ± 75 vs. 302 ± 63 W, ∆ -31 ± 41 W, ∆ -9 ± 10%, P = 0.017). The reduction in 5-min TT performance was significantly associated with durability of VT1 (rs = 0.719, P = 0.007). Durability of VT1 was not related to vastus lateralis carnosine content, citrate synthase activity, or complex I activity (P > 0.05).

Conclusion: These data provide the first direct support that durability of the moderate-to-heavy-intensity transition is an important performance parameter, as more durable athletes exhibited smaller reductions in 5-min TT performance following prolonged exercise. We did not find relationships between durability and vastus lateralis carnosine content, citrate synthase activity, or complex I activity.

Keywords: Durability; Exercise; Muscle.

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Conflict of interest statement

The authors declare no competing interests associated with this manuscript.

Figures

Fig 1
Fig 1
Schematic of the study design. TT, time trial; VT1, first ventilatory threshold
Fig 2
Fig 2
A Heart rate (HR), B rate of oxygen consumption (V̇O2), C energy expenditure (EE), D carbohydrate (CHO) oxidation rate, E fat oxidation rate and F muscle oxygen saturation (SmO2) during the prolonged phase of the POST trial. * denotes P ≤ 0.05, ** denotes P ≤ 0.01, *** denotes P ≤ 0.001
Fig 3
Fig 3
A Power output at the first ventilatory threshold (VT1), B 5-min time trial (TT) performance, C peak rate of oxygen consumption (V̇O2peak) and D muscle oxygen saturation (SmO2) at VT1 in the PRE and POST assessments. * denotes P ≤ 0.05
Fig 4
Fig 4
Relationships between A PRE-to-POST changes in VT1 and 5-min time trial (TT) performance, B PRE-to-POST changes VT1 and V̇O2peak, C PRE-to-POST changes in V̇O2peak and 5-min TT performance, and D peak fat oxidation rate (PFO) and PRE-to-POST changes in 5-min TT performance. Data are presented as Spearman’s rank-order correlation coefficients (rs) with P values and 95% confidence intervals.
Fig 5
Fig 5
Relationships between the PRE-to-POST change in VT1 power output and vastus lateralis: A carnosine concentration, B citrate synthase (CS) activity and C complex I activity. Data are presented as Spearman’s rank-order correlation coefficients (rs) with P values and 95% confidence intervals
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