Whilst the assessment of body composition is routine practice in sport, there remains considerable debate on the best tools available, with the chosen technique often based upon convenience rather than understanding the method and its limitations. The aim of this manuscript was threefold: (1) provide an overview of the common methodologies used within sport to measure body composition, specifically hydro-densitometry, air displacement plethysmography, bioelectrical impedance analysis and spectroscopy, ultra-sound, three-dimensional scanning, dual-energy X-ray absorptiometry (DXA) and skinfold thickness; (2) compare the efficacy of what are widely believed to be the most accurate (DXA) and practical (skinfold thickness) assessment tools and (3) provide a framework to help select the most appropriate assessment in applied sports practice including insights from the authors’ experiences working in elite sport. Traditionally, skinfold thickness has been the most popular method of body composition but the use of DXA has increased in recent years, with a wide held belief that it is the criterion standard. When bone mineral content needs to be assessed, and/or when it is necessary to take limb-specific estimations of fat and fat-free mass, then DXA appears to be the preferred method, although it is crucial to be aware of the logistical constraints required to produce reliable data, including controlling food intake, prior exercise and hydration status. However, given the need for simplicity and after considering the evidence across all assessment methods, skinfolds appear to be the least affected by day-to-day variability, leading to the conclusion ‘come back skinfolds, all is forgiven’.

In an attempt to better identify and inform the energy requirements of elite soccer players, we quantified the energy expenditure (EE) of players from the English Premier League (n = 6) via the doubly labeled water method (DLW) over a 7-day in-season period. Energy intake (EI) was also assessed using food diaries, supported by the remote food photographic method and 24 hr recalls. The 7-day period consisted of 5 training days (TD) and 2 match days (MD). Although mean daily EI (3186 ± 367 kcals) was not different from (p > .05) daily EE (3566 ± 585 kcals), EI was greater (p < .05) on MD (3789 ± 532 kcal; 61.1 ± 11.4 kcal.kg^-1 LBM) compared with TD (2956 ± 374 kcal; 45.2 ± 9.3 kcal.kg^-1 LBM, respectively). Differences in EI were reflective of greater (p < .05) daily CHO intake on MD (6.4 ± 2.2 g.kg^-1) compared with TD (4.2 ± 1.4 g.kg^-1). Exogenous CHO intake was also different (p < .01) during training sessions (3.1 ± 4.4 g.h^-1) versus matches (32.3 ± 21.9 g.h^-1). In contrast, daily protein (205 ± 30 g.kg^-1, p = .29) and fat intake (101 ± 20 g, p = .16) did not display any evidence of daily periodization as opposed to g.kg^-1, Although players readily achieve current guidelines for daily protein and fat intake, data suggest that CHO intake on the day before and in recovery from match play was not in accordance with guidelines to promote muscle glycogen storage.

Collagen peptide supplementation (COL), in conjunction with exercise, may be beneficial for the management of degenerative bone and joint disorders. This is likely due to stimulatory effects of COL and exercise on the extracellular matrix of connective tissues, improving structure and load-bearing capabilities. This systematic review aims to evaluate the current literature available on the combined impact of COL and exercise. Following Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines, a literature search of three electronic databases—PubMed, Web of Science and CINAHL—was conducted in June 2020. Fifteen randomised controlled trials were selected after screening 856 articles. The study populations included 12 studies in recreational athletes, 2 studies in elderly participants and 1 in untrained pre-menopausal women. Study outcomes were categorised into four topics: (i) joint pain and recovery from joint injuries, (ii) body composition, (iii) muscle soreness and recovery from exercise, and (iv) muscle protein synthesis (MPS) and collagen synthesis. The results indicated that COL is most beneficial in improving joint functionality and reducing joint pain. Certain improvements in body composition, strength and muscle recovery were present. Collagen synthesis rates were elevated with 15 g/day COL but did not have a significant impact on MPS when compared to isonitrogenous higher quality protein sources. Exact mechanisms for these adaptations are unclear, with future research using larger sample sizes, elite athletes, female participants and more precise outcome measures such as muscle biopsies and magnetic imagery.

Professional soccer players from the first team (1st team, n = 27), under twenty-one (U21, n = 21) and under eighteen (U18, n = 35) squads of an English Premier League soccer team were assessed for whole body and regional estimates of body composition using dual-energy X-ray absorptiometry (DXA). Per cent body fat was lower in 1st team (10.0 ± 1.6) compared with both U21 (11.6 ± 2.5, P = 0.02) and U18 (11.4 ± 2.6, P = 0.01) players. However, this difference was not due to variations (P = 0.23) in fat mass between squads (7.8 ± 1.6 v 8.8 ± 2.1 v 8.2 ± 2.4 kg, respectively) but rather the presence of more lean mass in 1st team (66.9 ± 7.1 kg, P < 0.01) and U21 (64.6 ± 6.5 kg, P = 0.02) compared with U18 (60.6 ± 6.3 kg) players. Accordingly, fat mass index was not different (P = 0.138) between squads, whereas lean mass index was greater (P < 0.01) in 1st team players (20.0 ± 1.1 kg · m⁻²) compared with U18 players (18.8 ± 1.4 kg · m⁻²). Differences in lean mass were also reflective of higher lean tissue mass in all regions, for example, upper limbs/lower limbs and trunk. Data suggest that training and nutritional interventions for younger players should therefore be targeted to lean mass growth as opposed to body fat loss.

The present study assessed changes in academy soccer players’ perception of mental fatigue (MF) across a competitive season, investigating the relationship between MF and other subjective measures of wellness. Ten players completed a modified Brief Assessment of Mood (BAM+) questionnaire that included the question: “How mentally fatigued do you feel”? on match-day (MD) and one (MD+1), two (MD+2) and three (MD+3) days post-match (35 matches). Players reported their MF, along with other subjective measures (sleep, muscle soreness, fatigue and motivation). Results found MF was elevated on MD+1 (43±1 mm) compared to all other days (all P≤0.001). Players reported lower MF on MD+1 in the late-season phase (34±2 mm) compared to both early- (50±2 mm, P≤0.001) and mid-season (46±2 mm, P≤0.001). This coincided with an 80%-win rate in the late-season phase versus the early- (33%) and mid-season (50%). There were very strong repeated-measures correlations between changes in MF and sleep (r=−0.77), muscle soreness (r=0.94), fatigue (r=0.92) and motivation (r=−0.89; all P ≤ 0.0005). In conclusion, MF was closely aligned to match success and other wellness variables. This data suggests a potential lack of sensitivity for identifying MF using a subjective questionnaire. Therefore, researchers and practitioners could work together to identify other ways of practically assessing MF.

This study examined if subjective wellbeing in soccer players was affected by match location, match result and opposition quality before a match (PRE), 1 day after (POST-1), and 3 days after a match (POST-3). Eleven professional male soccer players from the under 23 squad playing in the Premier League 2 division completed a wellbeing questionnaire before and after 17 matches. Match training load (session-rating perceived exertion) was not different, regardless of the location, result, or quality of opposition faced (P > 0.05). Subjective wellbeing was not different at PRE (P > 0.05); however, at POST-1 and POST-3, stress and mood were ≥20% lower after playing away from home or losing (P < 0.05). Stress, mood and sleep were ≥12% worse after playing against a higher-level opposition at POST-1. Coaches need to be aware that match location, match result and the quality of the opposition can influence post-match wellbeing, irrespective of match load.