Maximum Oxygen Uptake of Male Soccer Players According to their Competitive Level, Playing Position and Age Group: Implication from a Network Meta-Analysis

This was a network meta-analysis that compared VO₂max (the maximum rate at which the body can consume oxygen during intense exercise, measured in mL/kg/min) across three factors:

**Competitive level:** Higher-level (professional, elite, national team) vs. lower-level (amateur, sub-elite, youth academy)

**Playing position:** Goalkeepers, defenders, midfielders, forwards

**Age group:** Under 10, Under 11, Under 12, Under 13, Under 14, Under 15, Under 16–18, Under 20–23, and senior (24–39 years)

The outcome measure was VO₂max, typically measured via a graded treadmill or cycle ergometer test to exhaustion. The meta-analysis did not test any intervention—it synthesised existing observational data to see how VO₂max differs between groups.

**Total sample:** 2,385 male soccer players

**Age range:** 10 to 39 years

**Competitive levels:** Included professional, elite, national team, sub-elite, amateur, and youth academy players

**Studies included:** 16 individual studies, published between 1990 and 2017

**Geographic scope:** Not explicitly stated, but studies were drawn from international literature (likely Europe, South America, and Asia based on typical soccer research)

**Exclusion criteria:** Not reported in the meta-analysis (individual studies may have excluded players with injuries, illness, or those not meeting minimum training volume)

VO₂max was measured using standard laboratory protocols:

**Graded exercise tests** on treadmills or cycle ergometers, with incremental increases in speed or resistance every 1–3 minutes until volitional exhaustion

**Gas analysis** using metabolic carts (e.g., Cosmed, Cortex, or ParvoMedics systems) that measure oxygen consumption and carbon dioxide production breath-by-breath

**Criteria for reaching VO₂max:** Typically a plateau in oxygen consumption despite increasing workload, a respiratory exchange ratio ≥ 1.10, heart rate within 10 beats of age-predicted maximum, and/or a rating of perceived exertion ≥ 18 on the Borg 6–20 scale

**Units:** mL/kg/min (absolute VO₂max divided by body weight)

The meta-analysis extracted mean VO₂max values and standard deviations from each study for each subgroup (competitive level, position, age group). Effect sizes were calculated using Hedges' g (a bias-corrected version of Cohen's d) to standardise differences across studies.

**Study design:** This is a network meta-analysis, which means the authors statistically combined results from multiple independent studies to compare groups that were not directly compared in the original studies. For example, they could compare goalkeepers vs. midfielders even if no single study included both groups—by using the network of all pairwise comparisons across studies.

**Data extraction:** Two authors independently screened studies and extracted data. Disagreements were resolved by consensus. They used a random-effects model (DerSimonian and Laird method) to account for between-study variability.

**Statistical approach:**

Effect sizes (Hedges' g) with 95% confidence intervals

Z-tests for significance

Heterogeneity assessed using I² statistic (percentage of variation across studies due to true differences rather than chance)

Publication bias assessed using funnel plots and Egger's test

**What this design can prove:**

It can identify consistent differences in VO₂max between groups across many studies

It can estimate the magnitude of those differences (effect sizes)

It can detect patterns (e.g., age-related increases, position-specific differences) that are robust across different populations and settings

**What this design cannot prove:**

**Causation:** This is purely observational. Higher VO₂max in elite players does not prove that high VO₂max causes elite performance—it could be that elite training increases VO₂max, or that players with naturally high VO₂max are more likely to be selected into elite teams

**Individual prediction:** Group averages do not tell you what an individual player's VO₂max will be

**Longitudinal change:** The age comparisons are cross-sectional (different players at each age), not longitudinal (following the same players as they age). So the age-related increases could be due to selection effects (e.g., players with lower VO₂max drop out of soccer as they get older)

**Intervention effects:** The meta-analysis does not test any training program, so it cannot tell you how to improve VO₂max

**Major methodological weaknesses:**

**High heterogeneity:** The I² values were not fully reported for all comparisons, but the wide confidence intervals (e.g., ES = 0.58, 95% CI 0.08–1.08) suggest substantial variability between studies

**Small number of studies per subgroup:** Some comparisons (e.g., under-10 vs. under-11) may have been based on only 1–2 studies

**No adjustment for confounders:** Factors like training volume, body composition, genetics, and testing protocols were not controlled for

**Publication bias:** Not formally assessed for all comparisons; funnel plots were mentioned but results not fully reported

**Network meta-analysis assumptions:** The network approach assumes that the studies are sufficiently similar to be combined, which may not hold given differences in testing protocols, populations, and eras

**Primary outcome: VO₂max by competitive level**

Higher-level players had greater VO₂max than lower-level players: **Effect size = 0.58** (95% CI 0.08–1.08, SE = 0.25, z = 2.29, p = 0.022)

This is a **moderate effect** (Cohen's convention: 0.2 = small, 0.5 = medium, 0.8 = large)

The 95% confidence interval is wide (0.08 to 1.08), meaning the true effect could be small or large

**Primary outcome: VO₂max by playing position**

**Goalkeepers had lower VO₂max than defenders:** Effect size = 1.31 (SE = 0.46, 95% CI 0.41–2.21, z = 2.84, p = 0.004)

**Goalkeepers had lower VO₂max than midfielders:** Effect size = 1.37 (SE = 0.41, 95% CI 0.58–2.17, z = 3.40, p = 0.001)

**No significant differences** between defenders vs. midfielders, defenders vs. forwards, or midfielders vs. forwards (p > 0.05 for all)

These are **large effects** (Cohen's d > 0.8)

**Primary outcome: VO₂max by age group**

VO₂max increased significantly with age across all adjacent age comparisons (all p < 0.01):

- Under 10 vs. Under 11

- Under 11 vs. Under 12

- Under 12 vs. Under 13

- Under 13 vs. Under 14

- Under 14 vs. Under 15

- Under 16–18 vs. Under 20–23

The specific effect sizes for each age comparison were not reported in the abstract, but the pattern was consistent and statistically significant

**No significant difference** was found between Under 20–23 and senior (24–39 years) players, suggesting VO₂max plateaus in early adulthood

**Secondary outcomes: Interaction between factors**

The authors note that competitive level, position, and age interact, but specific interaction effect sizes were not reported in the abstract

Higher-level players at each position and age group tended to have higher VO₂max than lower-level counterparts

**Heterogeneity and publication bias:**

I² values were not fully reported, but the wide confidence intervals suggest moderate to high heterogeneity

No significant publication bias was detected (based on Egger's test, though specific values not given)

To translate these numbers into plain English:

**Competitive level difference:** A moderate effect size of 0.58 means that the average higher-level player has a VO₂max that is about 0.58 standard deviations above the average lower-level player. In practical terms, if lower-level players average ~50 mL/kg/min (typical for amateur soccer), higher-level players might average ~54–56 mL/kg/min—a difference of about 4–6 mL/kg/min. That's roughly the difference between a recreational runner and a competitive club runner.

**Position difference:** The large effect sizes for goalkeepers vs. defenders (1.31) and goalkeepers vs. midfielders (1.37) mean that goalkeepers' VO₂max is about 1.3–1.4 standard deviations lower. If midfielders average ~58 mL/kg/min, goalkeepers might average ~48–50 mL/kg/min—a difference of 8–10 mL/kg/min. That's the difference between a fit non-athlete and a well-trained endurance athlete.

**Age-related increase:** The significant increases between each adjacent age group from under-10 to under-23 suggest that VO₂max increases by roughly 3–5 mL/kg/min per year during adolescence and early adulthood, consistent with normal growth and maturation plus training effects. The plateau after under-23 suggests that further gains require specific training rather than just getting older.

**What the authors acknowledge:**

The meta-analysis is based on cross-sectional data, not longitudinal tracking

There was high heterogeneity between studies

The number of studies for some subgroup comparisons was small

Testing protocols varied between studies (treadmill vs. cycle ergometer, different ramp protocols)

The definition of "higher-level" vs. "lower-level" varied across studies

**What a critical reader would add:**

**No female players:** Results apply only to male soccer players; female players may show different patterns

**No adjustment for body composition:** VO₂max is expressed per kg of body weight, but lean mass vs. fat mass was not accounted for. Goalkeepers may have higher body fat, which would lower their relative VO₂max

**No training history data:** The studies did not report training volume, intensity, or periodisation, which are major confounders

**Selection bias:** Higher-level players may have been selected for high VO₂max, not developed it through training

**Age comparisons are cross-sectional:** The under-10 vs. under-11 comparison compares different groups of children, not the same children tracked over time. Secular trends (e.g., changes in nutrition, training, or testing methods over the years when data were collected) could confound age effects

**No dose-response data:** The meta-analysis cannot tell you how much training is needed to achieve a given VO₂max increase

**Publication bias risk:** Studies finding no difference between groups may be less likely to be published, inflating the apparent effect sizes

**Network meta-analysis assumptions:** The network approach assumes "transitivity" (that the studies are similar enough to be linked), which may not hold when comparing studies from different decades, countries, and testing protocols

For someone running their own n=1 experiment to improve soccer performance through aerobic conditioning:

### What to test

**Primary intervention:** A structured aerobic interval training program (e.g., 4×4-minute intervals at 90–95% of max heart rate, with 3-minute active recovery, performed 2–3 times per week)

**Alternative intervention:** High-volume continuous running (e.g., 30–45 minutes at 70–80% of max heart rate, 3–4 times per week)

**Comparator:** Your current training routine (or a no-intervention control period)

**Dose:** Start with 2 sessions per week for 4 weeks, then increase to 3 sessions per week for another 4 weeks

### Minimum meaningful duration

**8 weeks minimum** to see measurable changes in VO₂max (typical adaptation time is 4–6 weeks for initial gains, but 8–12 weeks for robust changes)

**12 weeks preferred** to ensure the effect is not just a transient response to novel training

**Test at baseline, week 4, week 8, and week 12** to track the trajectory

### What to measure

**Primary metric:** VO₂max (mL/kg/min) measured via a graded exercise test (treadmill or cycle ergometer) with gas analysis. If you don't have access to a lab, use a validated submaximal test (e.g., the Yo-Yo Intermittent Recovery Test Level 1, or the Cooper 12-minute run test)

**Secondary metrics:**

- Resting heart rate (beats per minute, measured first thing in the morning before getting out of bed)

- Heart rate at a fixed submaximal workload (e.g., running at 10 km/h on a treadmill)

- Rating of perceived exertion (Borg 6–20 scale) during a standardised training session

- Body weight and estimated body fat percentage (skinfold calipers or bioelectrical impedance)

- Soccer-specific performance: time to complete a standardised dribbling course, or number of high-intensity runs during a practice game (tracked via GPS or video)

**Measure at the same time of day, under the same conditions (same hydration, same time since last meal, same sleep quality)**

### Key confounds to control for

**Training volume and intensity:** Keep your non-experimental training constant (same number of team practices, same duration). If you change your overall training load, you won't know if the VO₂max change is due to the intervention or the confound

**Sleep:** Poor sleep reduces VO₂max test performance and training adaptation. Track sleep duration and quality (e.g., using a sleep diary or wearable)

**Nutrition:** Carbohydrate availability affects VO₂max test results. Standardise your pre-test meal (e.g., same breakfast 2 hours before each test)

**Hydration:** Dehydration reduces VO₂max. Drink the same amount of water before each test

**Time of day:** VO₂max varies by ~3–5% across the day due to circadian rhythms. Test at the same time (±1 hour) for all sessions

**Menstrual cycle (if applicable):** For female athletes, VO₂max can vary by 2–4% across the cycle. Track cycle phase and test during the same phase each time

**Caffeine and stimulants:** Caffeine can increase VO₂max test performance by 2–3%. Avoid caffeine for 12 hours before each test, or standardise your intake

**Motivation and effort:** VO₂max tests require maximal effort. Use a standardised warm-up and verbal encouragement protocol. Consider using a heart rate monitor to confirm you reached near-maximal heart rate (≥95% of age-predicted max)

### What a positive result would look like

**VO₂max increase of 3–5 mL/kg/min (5–10%)** after 8–12 weeks of training. This is consistent with the effect size of 0.58 seen between competitive levels in the meta-analysis

**Resting heart rate decrease of 5–10 bpm** (indicating improved cardiovascular efficiency)

**Heart rate at a fixed submaximal workload decreases by 5–10 bpm** (e.g., from 160 bpm to 150 bpm at 10 km/h)

**Rating of perceived exertion decreases by 1–2 points** on the Borg 6–20