Benjamin Samuels

This thesis quantifies the energy requirements of senior professional male soccer players across starting status and injury rehabilitation, while integrating practitioner perspectives on nutrition periodisation. Study 1 assessed 12 players over a 14-day in-season period using doubly labelled water (DLW), indirect calorimetry, and Actiheart 5. Resting energy expenditure (REE; mean difference = -0.12 ± 0.34 MJ·d–1) and total energy expenditure (TEE; -0.58 ± 1.16 MJ·d–1) were comparable between starters and nonstarters, with no significant differences in daily REE (all p > 0.59). Activity energy expenditure (AEE) varied daily and by starting status. Starters exhibited significantly higher AEE on match day (MD) versus MD-1 (+3.27 ± 0.60 MJ·d–1), MD+1 (+4.48 ± 0.81 MJ·d–1), and MD+2 (+4.51 ± 0.69 MJ·d–1; all p 0.06). Thus, nonstarters had significantly lower AEE than starters on MD (- 4.00 ± 0.64 MJ·d–1; p < 0.01), but significantly higher AEE on MD+1 (+2.61 ± 1.13 MJ·d–1; p = 0.02) and MD+2 (+2.03 ± 0.77 MJ·d–1; p = 0.01). These findings highlight that AEE is the most variable component of TEE in-season. Study 2 assessed three injured senior male players across 7-day periods of distinct rehabilitation phases. REE was comparable across phases (7.20–7.66 MJ·d–1), while TEE was lower during the immobilisation phase compared to the return to sport phase (-3.27 ± 2.53 MJ·d–1). AEE during immobilisation was lower than return to participation (-2.50 ± 0.33 MJ·d–1) and return to sport (-2.20 ± 0.41 MJ·d–1). Training days elicited significantly higher AEE than rest days (+2.84 ± 0.28 MJ·d–1; p < 0.01). Carbohydrate (CHO) intakes were not periodised from rest (3.3 ± 1.0 g·kg–1 ·d–1) to training days (3.1 ± 0.9 g·kg–1 ·d–1). These findings indicate that reduced AEE during immobilisation drives lower TEE, with an absence of change in dietary intake between phases or days. Study 3 explored nutrition periodisation practices via an online survey of 32 lead nutritionists (23 male, 9 female) working in professional male soccer. Ninety-one percent reported squad-wide nutrition periodisation, with UEFA CHO guidelines applied on MD-1 (100%) and MD (94%); but only 53% extended these to MD+1. Nonstarters and goalkeepers received tailored support in ~55% of clubs, while injured players received greater periodised nutrition support (94%). Insufficient nutrition staffing was identified as the main barrier (69%), while collaboration with catering (97%) and performance teams (91%) were key enablers. Collectively, this thesis provides new insights into the energy demands of senior professional male soccer players during contextual periods, as well as the implementation of nutrition periodisation. These findings offer practical guidance for the development of periodised nutrition guidelines for elite male soccer.

The purpose of this study was to quantify the total energy expenditure (TEE) of international female rugby union players. Fifteen players were assessed over 14-days throughout an international multi-game tournament, which represented two consecutive one-match microcycles. Resting metabolic rate (RMR) and TEE were assessed by indirect calorimetry and doubly labelled water, respectively. Physical activity level (PAL) was estimated (TEE:RMR). Mean RMR, TEE, and PAL were 6.60 ± 0.93 MJ.day-1, 13.51 ± 2.28 MJ.day-1 and 2.0 ± 0.3 AU, respectively. There was no difference in TEE (13.74 ± 2.31 vs. 13.92 ± 2.10 MJ.day-1; p = 0.754), or PAL (2.06 ± 0.26 AU vs. 2.09 ± 0.23 AU; p = 0.735) across microcycles, despite substantial decreases in training load (total distance: -8088 m, collisions: -20 n, training duration: -252 min). After correcting for body composition, there was no difference in TEE (13.80 ± 1.74 vs. 13.16 ± 1.97 adj. MJ.day-1, p = 0.190), RMR (6.49 ± 0.81 vs. 6.73 ± 0.83 adj. MJ.day-1, p = 0.633) or PAL (2.15 ± 0.14 vs 1.87 ± 0.26 AU, p = 0.090) between forwards and backs. For an injured participant (n = 1), TEE reduced by 1.7 MJ.day-1 from pre-injury. For participants with illness (n = 3), TEE was similar to pre-illness (+0.49 MJ.day-1). The energy requirements of international female rugby players were consistent across one-match microcycles. Forwards and backs had similar adjusted energy requirements. These findings are critical to inform the dietary guidance provided to female rugby players.

Abstract

Body composition assessments in professional male football often lack sport-specific evidence, risking mismanagement of player health and performance. This study described dual-energy X-ray absorptiometry (DXA)-derived values by playing position, ethnicity, competition level, and seasonal timepoints. A total of 343 players (mean ± SD: age = 22.6 ± 4.6 years; stature = 182.0 ± 6.9 cm; body mass = 79.1 ± 8.6 kg) from the English Premier League (n = 76) and English Football League (n = 267) completed 939 scans over a 10-year period (2014–2024) using DXA (Lunar iDXA, GE Healthcare), with repeat measurements taken across the season. Players were sub-classified as Goalkeepers (n = 32), Central Defenders (n = 55), Wide Defenders (n = 64), Central Midfielders (n = 73), Wide Midfielders (n = 62), and Forwards (n = 57). Body composition ranges specific to position were identified for bone mass (3.5–4.2 kg), lean mass (61.2–69.6 kg), fat mass (9.1–13.5 kg), and percentage body fat (11.6–15.4%). Significant differences in bone, lean, and fat mass were observed between playing positions, ethnicity, and league level ( p  < 0.050). Across a single season, fat-free mass increased significantly, while fat mass decreased (both: p  < 0.001), indicating positive physiological adaptations from moderate body mass increases rather than performance concerns. These findings indicate that body fat values above the commonly cited < 10% threshold are regularly observed in elite male footballers, suggesting the need for more individualised targets over generic team-wide standards. Providing the largest criterion-measured dataset for professional male footballers, this study supports athlete-centred, position-specific decision-making to optimise player health and performance.

Body composition assessments in professional male football often lack sport-specific evidence, risking mismanagement of player health and performance. This study described dual-energy X-ray absorptiometry (DXA)- derived values by playing position, ethnicity, competition level, and seasonal timepoints. A total of 343 players (mean±SD: age=22.6±4.6 years; stature=182.0±6.9 cm; body mass=79.1±8.6 kg) from the English Premier League (n=76) and English Football League (n=267) completed 939 scans over a 10-year period (2014–2024) using DXA (Lunar iDXA, GE Healthcare), with repeat measurements taken across the season. Players were sub-classified as Goalkeepers (n=32), Central Defenders (n=55), Wide Defenders (n=64), Central Midfielders (n=73), Wide Midfielders (n=62), and Forwards (n=57). Body composition ranges specific to position were identified for bone mass (3.5–4.2 kg), fat-free soft tissue mass (61.2–69.6 kg), fat mass (9.1–13.5 kg), and percentage body fat (11.6– 15.4%). Significant differences in bone, fat-free soft tissue, and fat mass were observed between playing positions, ethnicity, and league level (p<0.050). Across a single season, fat-free soft tissue mass increased significantly, while fat mass decreased (both: p<0.001), indicating positive physiological adaptations from moderate body mass increases rather than performance concerns. These findings indicate that body fat values above the commonly cited<10% threshold are regularly observed in elite male footballers, suggesting the need for more individualised targets over generic team-wide standards. Providing the largest criterion-measured dataset for professional male footballers, this study supports athlete-centred, position-specific decision-making to optimise player health and performance.

This is the first study to assess longitudinal changes in anthropometric, physiological, and physical qualities of international women’s rugby league players. Thirteen forwards and 11 backs were tested three times over a 10-month period. Assessments included: standing height and body mass, body composition measured by dual x-ray absorptiometry (DXA), a blood panel, resting metabolic rate (RMR) assessed by indirect calorimetry, aerobic capacity (i.e.,V˙O2max) evaluated by an incremental treadmill test, and isometric force production measured by a force plate. During the pre-season phase, lean mass increased significantly by ~2% for backs (testing point 1: 47 kg; testing point 2: 48 kg) and forwards (testing point 1: 50 kg; testing point 2: 51 kg) (p = ≤ 0.05). Backs significantly increased their V˙O2max by 22% from testing point 1 (40 ml kg-1 min-1) to testing point 3 (49 ml kg-1 min-1) (p = ≤ 0.04). The V˙O2max of forwards increased by 10% from testing point 1 (41 ml kg-1 min-1) to testing point 3 (45 ml kg-1 min-1), however this change was not significant (p = ≥ 0.05). Body mass (values represent the range of means across the three testing points) (backs: 68 kg; forwards: 77–78 kg), fat mass percentage (backs: 25–26%; forwards: 30–31%), resting metabolic rate (backs: 7 MJ day-1; forwards: 7 MJ day-1), isometric mid-thigh pull (backs: 2106–2180 N; forwards: 2155–2241 N), isometric bench press (backs: 799–822 N; forwards: 999–1024 N), isometric prone row (backs: 625–628 N; forwards: 667–678 N) and bloods (backs: ferritin 21–29 ug/L, haemoglobin 137–140 g/L, iron 17–21 umol/L, transferrin 3 g/L, transferring saturation 23–28%; forwards: ferritin 31–33 ug/L, haemoglobin 141–145 g/L, iron 20–23 umol/L, transferrin 3 g/L, transferrin saturation 26–31%) did not change (p = ≥ 0.05). This study provides novel longitudinal data which can be used to better prepare women rugby league players for the unique demands of their sport, underpinning female athlete health.