The Effect of the Aerodynamic Time-Trial Position on Gross Efficiency and Self-Paced Time-Trial Performance
Twelve participants rode 20-minute self-paced time trials in the aerodynamic position at torso angles of 0°, 12° and 24°, with gross efficiency measured before and after. Gross efficiency was lower at 0° than at 24° and fell after every time trial, but the size of that fall did not differ between angles. Mean time-trial power was significantly higher at 24° than at 12° and 0°.
The authors conclude that lowering the torso reduces physiological and metabolic performance at submaximal and time-trial intensity, leaving a trade-off between physiological functioning and aerodynamic drag.
Participants
n=12 (abstract: "Twelve participants"). Sex, age, training status and fitness values are not given in the abstract.
Protocol
Visit 1: incremental exercise test to find the power at maximal pulmonary oxygen uptake.
Visits 2 to 4: 20-minute self-paced time trial in the aerodynamic time-trial position, one torso angle per visit (0°, 12°, 24°), with gross efficiency (GE) tests before and after.
The aerodynamic position was systematically controlled; only the torso angle changed.
Key Results
| Comparison | Result |
|---|---|
| GE, 0° vs 24° torso angle | Lower at 0° (P = 0.039) |
| GE, after vs before the time trial | Lower after (P < 0.001) |
| Decline in GE between angles | No significant difference |
| Mean time-trial power, 24° vs 12° | Higher at 24° (P = 0.012) |
| Mean time-trial power, 24° vs 0° | Higher at 24° (P = 0.007) |
GE vs mean time-trial power (all angles pooled): R = 0.337, R2 = 0.114, P = 0.044.
Relative torso angle vs mean time-trial power: R = 0.374, R2 = 0.140, P = 0.025.
The abstract gives no power or GE values in watts or percent for any position.
Practical Application
In 12 participants riding 20-minute self-paced time trials, mean power was significantly higher with a 24° torso angle than at 12° (P = 0.012) or 0° (P = 0.007), and gross efficiency was lower at 0° than at 24° (P = 0.039); the authors conclude that a lower torso costs physiological performance, a trade-off against the drag it saves. A lower, flatter torso lowers the power you can hold for about 20 minutes; whether the drag saving pays for it was not measured.
Gross efficiency fell during every time trial, but a low torso did not make that fall steeper; the cost of the low position is in the level, not in a faster fade over 20 minutes.
Inference, not tested here: the lowest position is only worth it if its drag saving exceeds the power lost; set the torso from a ridden test of power in each position together with a drag estimate, not from how aggressive it looks.
The correlations are weak (R2 = 0.114 and 0.140): torso angle and efficiency explain only a small part of the differences in time-trial power between rides.
Limitations
Laboratory ergometer; no drag measurement, so the net effect on speed is unknown.
Participant characteristics are not in the abstract; order of the three positions and familiarisation not described.
Journal not indexed in PubMed; the abstract comes from the Crossref record.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level
within-subject comparison of three positions, n=12
Full text (checked 2026-10-12)
Participants were twelve well trained cyclists experienced in the aerodynamic position (10 male, 2 female) with at least two years of training and racing: age 31 ± 10 years, V̇O₂max 68.6 ± 10.2 ml·kg⁻¹·min⁻¹, power at V̇O₂max 392 ± 49 W (5.8 ± 0.8 W·kg⁻¹), preferred torso angle 12.7 ± 6.4° (full text, Table 1).
The three torso angles were ridden in randomised order on an adjustable time-trial bike with arm rests 8 cm apart; three of the twelve could not reach 0° and used their smallest reachable angle, between 1° and 2.4° (full text).
Each visit: 6 min at 100 W, 6 min at 45% of power at V̇O₂max, GE at 55% (216 ± 27 W), 3 min rest, the self-paced 20-min time trial with only elapsed time shown, then 3 min at 100 W and a 10-min post-GE bout at 55% at the same cadence (full text).
GE before the time trial was 21.77 ± 1.01% at 0°, 22.10 ± 0.73% at 12° and 22.57 ± 1.11% at 24°, and fell after the time trial at all angles (main effect of time F = 63.48, ηp2 = 0.85) (full text).
Torso angle had a large main effect on time-trial power (F = 12.37, ηp2 = 0.53) and an effect on RPE (F = 5.73), but none on heart rate (F = 0.07, P = 0.94), and end-of-trial blood lactate did not differ between angles (P = 0.65) (full text, Table 2).
The authors estimate that the lower GE at 0° would cost nearly 63 seconds over a 40-km time trial, against a 14% reduction in frontal area from 24° to 0° reported with the same method, and conclude the losses "would likely be offset" by aerodynamic savings in a field time trial (full text).
In this study GE explained only 11% of the variation in time-trial power, versus around 30% in an earlier analysis of several studies (full text).