Table 3.
Summary of experimental studies investigating the response of hormones of the hypothalamic-pituitary-ovarian axis with divergent amounts of energy availability
| Study | LEA Induction Method | Population | LEA Duration (days) | EI | EEE | EA | Exercise Mode | Dietary Composition: (Pro, CHO, Fat %) | LH | E2 | FSH | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Loucks and Heath (1994a, b) | REI Only | Y, SED (N = 7 F) | 4† | 10 and 43 | 0 | 10 and 43 | N/A | 15, 55, 30% | ↓ pulse freq., ↑ amp. in LEA | ⟷§ | ⟷§ | |
| Loucks, Verdun and Heath (1998) | EX Only | Y, SED (N = 9 F) | 4† | 37 and 70 | 24 | 13 and 46 | Running @ 70% VO2max | 15, 55, 30% | ↓ pulse freq., ↑ amp. in LEA | ⟷ § | ↑ (24 h ) | |
| Loucks and Thuma (2003) | REI and EX (3 × 2 Exp. Design) | Y, SED (N = 29 F) | 5† | 25, 35, 45 and 60 | 15 | 10, 20, 30 and 45 | Running @ 70% VO2max | 15, 57, 28% | ↓ pulse freq., ↑ amp in LEA < 30 |
↓ 10 vs 45 (24 h ) |
⟷ § | |
| Loucks and Verdun (1998) | REI and EX | Y, SED (N = 8 F) | 5 (+ 1-day RF) | 22 (+ 89 RF day) | 15 | 10 (+ 77 RF day) | Running @ 70% VO2max | 15, 55, 30% |
↓ pulse freq., ↑ pulse amp. in LEA Partial restoration of pulsatility with 1-day RF, ⟷ amplitude |
⟷ § | NA | |
| Loucks (2006) | REI and EX | SED (N = 19 F; 9 ADOL, 10 ADULT) | 5† | 25 and 60 | 15 | 10 and 45 | Running @ 70% VO2max | 15%, 57%, 28% | ↓ pulse freq. and mean 24 h in LEA in ADOL only | ⟷ § | NA | |
Arrows represent changes in groups with low energy availability (typically lower than 40–45 kcal/kg lean body mass/day). A graphical summary of the contents of the table can be seen in Fig. 3
ADOL adolescents, ADULT adults, amp. amplitude, CHO carbohydrates, CON control, EA energy availability, EEE exercise energy expenditure, EI energy intake, ET endurance Trained, EX exercise, ET endurance-trained, F female, freq. frequency, HI high intensity, LEA low energy availability, LI low intensity, M male, NA not assessed, NEA normal energy availability, Pro protein, REI restricted energy intake, RIR repetitions in reserve, RF refeeding, RT resistance-trained, SED sedentary, Y young. EA, EI and EEE are reported as kcal/kg LBM/day. Morning blood values are differentiated with §, in studies with serial blood sampling, which also report 24 h transverse means (24 h ) in selected parameters
†Sampling/measurements were performed on the 5th or 6th day where the serial blood sampling was performed during 24 h