Table 4.

Summary of studies investigating the effects of energy availability on markers of bone metabolism

Study	LEA induction method	Population	LEA duration (days)	EI	EEE	EA	Exercise mode	Dietary composition (Pro, CHO, Fat %)	Bone formation markers	Bone resorption markers
Ihle and Loucks (2004)	REI and EX (3 × 2 Exp. Design)	Y, SED (N = 29 F)	5	25, 35, 45 and 60	15	10, 20, 30 and 45	Uphill walking @ 70% VO2max	15, 57 and 28%	Linear ↓ in P1CP as EA decreased Curvilinear ↓ in OC, greatest between 30 – 20 LEA treatments	NTx ↑ in 10 LEA condition
Papageorgiou et al (2017)	REI and EX	Y, ACTIVE (N = 22; 11 M, 11 F)	5	30 and 60	15	15 and 45	Running @ 70% VO2max	~ 18, 48 and 34%	P1NP ↓ in F during LEA, ⟷ in M ⟷ in Sclerostin between conditions in M or F	β-CTX ↑ in F during LEA, ⟷ in M
Papageorgiou et al (2018)	REI Only; EX only	Y, ACTIVE (N = 10 F)	3	15, 45 and 45	0, 30 and 0	5, 15 and 45	Running @ 70% VO2max (LEA (EX) only)	20, 50 and 30%	P1NP ↓ in LEA (Diet) compared to CON	⟷ in β-CTX
Murphy and Koehler (2020)	REI only	Y, RT (N = 7; 5 M, 2 F)	3	15, 15 and 40	0 (days 1—2) REX on day 3 (EEE NR)	0, 0 and 40	5 × 5 Back Squats @ ~ 1 RIR	38, 50, 12% (LEA) 14, 60, 26% (NEA)	⟷ in P1NP ↑ Sclerostin prior to REX bout, restored post-REX	NA

A graphical summary of the contents of the table can be seen in Fig. 3

Arrows represent changes in groups with low energy availability (typically lower than 40–45 kcal/kg lean body mass/day)

EA energy availability, LEA low energy availability, EI energy intake, EEE exercise energy expenditure, CHO carbohydrates, PRO protein, M male, F female, ET endurance-trained, NA not assessed, NEA normal energy availability, REI reduced energy intake, REX resistance exercise, RT resistance-trained, Y young, P1CP carboxy-terminal propeptide of type 1 procollagen, P1NP N-terminal propeptide of type 1 procollagen, NTx aminoterminal telopeptide of type 1 collagen, β-CTX C-terminal telopeptide of type 1 collagen, OC Osteocalcin