Isabel Guisado-Cuadrado

Bone mineral density (BMD) is a key indicator of bone health, influenced by factors like exercise or energy availability. While exercise generally benefits BMD, sports with varied, dynamic movements (team/power-based sports) seem more effective than endurance modalities, characterized by repetitive, cyclic movements with low intensity. Thus, this scoping review aimed to examine and reflect on whole-body, spine, and femoral neck BMD values reported in the literature, categorized by specific sport modalities. Following PRISMA 2020 and PRISMA-ScR guidelines, a systematic search was conducted in January 2024 using PubMed, Scopus, and Web of Science, yielding 4711 studies. After screening, 111 studies were included, encompassing a total of 6058 participants across 60 distinct sport modalities in the final review. Studies were selected based on specific inclusion criteria, including healthy females and males aged 18–35 years and playing any sport classified from Tier 2–5 according to the Participation Classification Framework. Of the groups above the weighted mean for whole-body BMD, 83.7% of males and 76.3% of females were involved in team/power-based sports. For spine BMD, 9.1% of males and 12.9% of females engaged in team/power-based sports were below the weighted mean. For the femoral neck, 95.8% of males and 86.7% of females’ groups below the weighted mean were involved in individual sports. Overall, team/power-based sports characterized by dynamic, multidirectional loading are associated with higher bone mineral density, whereas exclusive participation in individual/endurance-based sports—often involving lower mechanical stimuli—may be linked to lower bone mineral density, highlighting the importance of sport-specific loading characteristics for bone health.

Low energy availability (LEA) occurs when dietary energy intake is insufficient to meet the combined demands of exercise and essential physiological functions. Problematic LEA is recognized as the primary driver of Relative Energy Deficiency in Sport (RED‐S), but the short‐term physiological consequences of LEA remain less clearly defined. Thus, this systematic review aimed to synthesize evidence from experimental studies examining the short‐term effects of experimentally induced LEA on biochemical markers in athletic populations. A systematic search was conducted in PubMed, Web of Science, and Scopus in accordance with PRISMA guidelines. Eligible studies included experimental designs, with pre–post assessments of an LEA intervention (> 24 h). Outcomes included biomarkers of bone metabolism, calcium metabolism, energy regulation, inflammation, iron status, sex hormones, and thyroid function. Thirteen studies (145 participants) were included. Approximately half of the interventions reported significant increases in βCTX‐1 and reductions in P1NP. Leptin consistently decreased following LEA, whereas IGF‐1 and T3 remained stable in most studies, and testosterone decreased in 50% of interventions. No consistent changes were observed in estradiol, progesterone, calcium metabolism, inflammatory markers, or iron status. Short‐term experimentally induced LEA elicits early endocrine and metabolic adaptations, particularly affecting bone remodeling, leptin, and testosterone. However, these responses should be interpreted in the context of the frequent coexistence of low carbohydrate availability, which may contribute to or exacerbate the observed effects. These findings emphasize the relevance of monitoring key biochemical markers during periods of potential LEA risk and underscore the need for standardized, sex‐specific protocols in future research.

Bone metabolism is a dynamic process regulated by systemic and local factors, including sex hormones. While in vitro studies suggest that hormonal fluctuations impact bone biomarkers, in vivo findings remain inconsistent. Therefore, this systematic review aimed to evaluate whether biochemical markers of bone resorption and bone formation fluctuate across different phases of the menstrual cycle in healthy regular menstruating females. Following PRISMA guidelines, a comprehensive search was conducted in PubMed and Web of Science (January 2025). A total of 18 studies were included and assessed for quality using the NHLBI Quality Assessment Tool. Considerable heterogeneity was found across studies in design, phase classification, and outcome reporting. While 5 out of 7 studies on β-CTX-I reported lower concentrations during the luteal phase, 6 out of 8 studies showed that osteocalcin concentrations did not vary across the MC. Findings concerning other biomarkers included in this review were limited and inconsistent, hindering the identification of a clear trend. Current evidence does not establish a consistent pattern in bone metabolism biomarker fluctuations across the MC. Variability in methodology, hormone verification, and participant characteristics may contribute to these inconsistencies. PROSPERO registration CRD42022375821.

Purpose : To compare energy expenditure (EE), carbohydrate (CHOx), and fat oxidation (FatOx) during a high-intensity interval exercise across the early follicular, late follicular, and mid-luteal phases of the menstrual cycle (MC); the active pill (APP) and withdrawal (WP) phases of the oral contraceptive (OC) cycle; and in postmenopausal females (POS). Methods : Twenty-four eumenorrheic females, 18 OC users and 13 POS completed a standardized high-intensity interval running protocol (8 × 3 min at 85% vVO ₂ peak). Eumenorrheic participants were tested in the early follicular phase, late follicular phase, and mid-luteal phase; OC users in the APP and WP; and POS once. Hormonal phases were verified by circulating 17 β -oestradiol and progesterone. EE, CHOx, and FatOx were quantified using indirect calorimetry. Results : EE and substrate oxidation did not differ across the MC phases (all P > .05). CHOx was slightly lower during APP than WP ( P = .025; mean difference = 123 mg·min ⁻¹ ). FatOx was lower in POS compared with late follicular phase ( P = .03; mean difference = 92 mg·min ⁻¹ ) and mid-luteal phase ( P = .039; mean difference = 89 mg·min ⁻¹ ). Conclusion : Hormonal fluctuations during the MC have minimal impact on EE or substrate oxidation during exercise, suggesting their measurements do not need to be adjusted according to MC phases. However, small but significant differences were found between phases of the OC cycle, with lower CHOx during the APP compared to the WP. Finally, POS exhibit lower FatOx than eumenorrheic females.

Purpose : This study aimed to investigate phase-specific symptom patterns across the menstrual and hormonal contraceptive (HC) cycles in exercising females. A total of 42 participants were initially screened; eight were excluded due to not meeting hormonal criteria for eumenorrheic status, resulting in a final sample of 20 eumenorrheic and 14 HC users. Participants completed the Daily Record of Severity of Problems questionnaire daily over one hormonal cycle. Hormonal profiles were verified through serum hormone analysis. Symptom data were analyzed by grouping days into hormonal phases. Results : In eumenorrheic females, symptom severity peaked during the early follicular and late luteal phases, particularly in mood, behavior, and pain dimensions. The ovulatory, early luteal, and midluteal phases were the most stable, with minimal symptom expression. In contrast, HC users showed fewer fluctuations, though pain-related symptoms increased during the withdrawal bleeding phase. When comparing groups, eumenorrheic participants reported significantly more intense and frequent symptoms across all phases, especially in behavior and impairment dimensions during bleeding and late luteal phase. Conclusions : These findings highlight the importance of monitoring menstrual beyond the bleeding phase, as key symptomatology arises in less visible phases, such as the late luteal phase. Moreover, the relative stability observed in ovulatory, early luteal, and midluteal phases may represent favorable phases for athletic performance, given the minimal presence of adverse symptoms. HC use appears to attenuate but not suppress symptoms.

The aim of the study was to analyze the influence of an aerobic fitness level on the percentage of maximum oxygen consumption, heart rate, and power output (%VO_2max, %HR_max, and %W_max) at which ventilatory thresholds 1 (VT1) and 2 (VT2) occur during a ramp incremental cycle‐ergometer test in males and females considering age. 1450 males and 241 females performed a ramp incremental exercise test until exhaustion to determine VT1, VT2, and VO_2max. Combining the oxygen consumption at VT1, VT2, and VO_2max by clustering analysis, males were classified as a low, medium, or high aerobic fitness level and females were classified as a low or high aerobic fitness level. Results showed VO_2max was very poorly correlated with the %VO_2max at which VT1 and VT2 occur (r ≤ 0.115), whereas oxygen consumption at VT1 and VT2 showed a stronger positive association with the %VO_2max at which VT1 and VT2 occur, respectively (r = 0.357–0.604). Furthermore, the %VO_2max at which VT1 and VT2 occur were greater the higher the aerobic fitness level (all p ≤ 0.002), observing a high heterogeneity in the %VO_2max at which VT1 and VT2 occur even stratifying the sample by sex and aerobic fitness levels. In conclusion, the percentage of maximum at which VT1 and VT2 occur are better related to oxygen consumption at VT1 and VT2, respectively, than to VO_2max. Moreover, the common strategy consisting of establishing exercise intensity as a fixed percentage of maximum might not be effective to match intensity across individuals even if sex and aerobic fitness levels is considered.Trial Registration: NCT06246760.

Purpose To investigate the acute effects of eccentric-based resistance exercise and sex-hormone fluctuations on P1NP and β-CTX-1 concentrations in premenopausal females. Methods Nine eumenorrheic females and ten oral contraceptive (OC) users performed eccentric-based resistance exercise, consisted of 10 × 10 repetitions of parallel back squats with a 4-s eccentric phase, in the early-follicular (EFP), late-follicular (LFP) and mid-luteal (MLP) phases of the menstrual cycle (MC) or in the withdrawal (WP) and active pill-taking (APP) phases of the OC cycle. Results 17β-oestradiol (pg·ml⁻¹) was lower in EFP (36.63 ± 29.93) compared to LFP (224.81 ± 233.81; p ≤ 0.001) and MLP (161.45 ± 110.08; p < 0.001) and higher in WP (24.857 ± 29.428) compared to APP (12.72 ± 13.36; p = 0.004). Progesterone (ng·ml-1) was higher in MLP (8.30 ± 5.23) compared to EFP (0.33 ± 0.33; p < 0.001) and LFP (0.21 ± 0.18; p < 0.001), no significant differences were observed between the WP and APP. In eumenorrheic females, β-CTX-1 (ng·ml⁻¹) was lower in MLP (0.395 ± 0.126) compared to LFP (0.472 ± 0.137; p = 0.044). Comparing MC vs OC phases, eumenorrheic females had higher P1NP levels (ng·ml⁻¹) compared to OC users: EFP (62.54 ± 13.13) vs APP (50.69 ± 8.91; p = 0.034), LFP (67.32 ± 18.96) vs WP (52.16 ± 10.72; p = 0.047), LFP vs APP (p = 0.025), MLP (67.51 ± 19.34; p = 0.049) vs WP, MLPvsAPP (p = 0.027). Exercise time effect showed lower β-CTX-1 concentrations 2 h post-exercise (MC: 0.376 ± 0.114, p < 0.001; OC: 0.340 ± 0.156, p = 0.030) compared to pre-exercise (MC: 0.485 ± 0.137; OC: 0.428 ± 0.188) in all participants. Conclusions β-CTX-1 concentrations were lower in the mid-luteal phase, emphasising the importance of standardizing bone marker measurements to a specific MC phase. OC users exhibited reduced P1NP levels, underscoring the need to investigate synthetic and endogenous hormones’ impact on long-term bone structure and strength. Trial registration The study was registered at Clinicaltrials.gov NCT04458662 on 2 July 2020.

The first aim was to explore the difference in metabolic flexibility between sexes in response to changing exercise intensity under control conditions. The second aim was to evaluate metabolic flexibility between sexes in response to exercise intensity adding two different metabolically challenging stimuli (glycogen depletion and heat). Eleven males (22 ± 3 years, 176.2 ± 4 cm, 68.4 ± 4.9 kg, and 60.2 ± 4.1 mL/kg FFM/min) and nine females (22 ± 2 years, 166.7 ± 4.5 cm, 61.9 ± 2.9 kg, and 64.2 ± 5.6 mL/kg FFM/min) performed a maximal incremental exercise test (30 W every 3 min) on a cycle ergometer under three conditions: control (24 h high-carbohydrate diet followed by the incremental test), glycogen depletion (glycogen-depletion protocol followed by 24 h low-carbohydrate diet and then the incremental test), and heat (24 h high-carbohydrate diet followed by 30 min passive heating and then the incremental test in heat). In the last minute of each step, lactate was analysed, fat (FATox/FFM) and carbohydrate oxidation (CHox/FFM), and energy expenditure (EE/FFM) normalized to fat-free mass (FFM) was estimated by indirect calorimetry. Females presented a greater FATox/FFM as exercise intensity increases across conditions (control, glycogen depletion, and heat) ( p = 0.006). In contrast, CHox/FFM was not significantly different between sexes at any specific intensity across conditions ( p > 0.05). Consequently, EE/FFM was higher in females throughout the different intensities across conditions ( p = 0.002). Finally, lactate concentration was not different between sexes at the same intensities across conditions ( p = 0.87). In conclusion, females present a greater metabolic flexibility, due to the higher FATox/FFM throughout the different intensities, regardless of whether the test is performed in conditions emphasizing the oxidative pathway (glycogen depletion) or the glycolytic pathway (heat). Clinical trials: NCT05703100