Why Less Fuel Doesn't Equal Better Performance
- projectunlaced
- Aug 20
- 2 min read
Athletes sometimes intentionally lower their energy availability for short periods to reduce body weight. The goal is often to improve their power-to-mass ratio and overall performance. This study aimed to examine how 10 days of low energy availability (LEA) followed by 2 days of optimal energy availability (OEA) affected physical performance in trained women. In addition, physiological indicators were assessed, both at the whole-body and molecular levels, that are linked to performance.
Methods
30 young trained eumenorrheic (having a regular menstrual cycle) were randomly assigned to either 10-day Low Energy Availability (LEA) protocol or an Optimal Energy Availability (OEA) protocol.
Prior to the 10-day intervention, all participants did 5 days with OEA.
Following the 10-day intervention, participants completed 2 days of an OEA protocol.
Assessments include muscle biopsies, blood sampling, physical performance tests, body composition measurements, and resting metabolic rate measurements. The sprint test consisted of 5x6sec maximum effort on the bike with 24sec recovery in between.
Results
The average sprint power and mean peak power output decreased in the LEA group.
Even after the OEA recovery period, performance in the sprint test was still inferior to the OEA control group.
The average power in the 4-minute bike time trial decreased by 5.4% in the LEA group.
Muscle glycogen content decreased in the LEA group. This is important because muscle glycogen is the main source of energy for muscles.
Resting Energy Expenditure (REE) decreased in the LEA group.
LEA reduced glucose levels. Glucose is your body's main source of quick energy so lower levels can mean your body has less readily available fuel.
LEA reduced Sex Hormone-Binding Globulin (SHBG). This protein binds to sex hormones (like estrogen and testosterone). Lower levels can disrupt hormone balance and may signal energy stress.
LEA reduced androgen index, an estimate of the amount of active testosterone in the body.
LEA raised the cortisol/insulin ratio. This suggests that the body is leaning towards a stressed state rather than a building/recovery state.
Conclusions
Ten days of low energy availability (LEA) led to declines in absolute physical performance, accompanied by a drop in muscle glycogen stores. Although two days of optimal energy availability (OEA) during recovery helped reverse some of these effects, performance levels remained below those seen with OEA. These results challenge the idea that slight body mass reductions from LEA enhance the power-to-mass ratio and, in turn, boost performance.
Citations
Oxfeldt M, Marsi D, Christensen PM, Andersen OE, Johansen FT, Bangshaab M, Risikesan J, Jeppesen JS, Hellsten Y, Phillips SM, Melin AK, Ørtenblad N, Hansen M. Low Energy Availability Followed by Optimal Energy Availability Does Not Benefit Performance in Trained Females. Med Sci Sports Exerc. 2024 May 1;56(5):902-916. doi: 10.1249/MSS.0000000000003370. Epub 2023 Dec 27. PMID: 38181220.