High-Intensity Demands of 6-a-Side Small-Sided Games and 11-a-Side Matches in Youth Soccer Players

Metabolic Power in Team and Racquet Sports: A Systematic Review with Best-Evidence Synthesis

Background

In intermittent team and racquet sports, metabolic loads are rarely investigated as they are difficult to examine, e.g., by portable metabolic carts and lactate measures. However, determining the instantaneous metabolic power of intermittent running from acceleration and speed data is possible. Recently, this potential has gained more interest in research and practice due to the development of player tracking technologies that allow easy access to the required data. The aim of this review was to systematically investigate the validity and point out the evidence of this new approach for estimating metabolic loads in intermittent sports. To provide an in-depth understanding of this approach and its validity, the fundamental aspects of the underlying concept were also considered.

Methods

PubMed®, Cochrane Library, Web of Science™, and BISp-surf databases were included in the search conducted on March 1, 2021. Studies assessing physiological and methodological validation as well as conceptual studies of the metabolic power approach in intermittent sports players without diseases or injuries were deemed eligible. The quality assessment was implemented using a modified 12-item version of the Downs and Black checklist. Additionally, a best-evidence synthesis of the validation studies was performed to clarify the direction and strength of the evidence.

Results

Of 947 studies that were identified, 31 met the eligibility criteria of which 7 were physiological, 13 methodological validation, and 11 conceptual studies. Gold standards for validating the metabolic power approach were predominantly oxygen uptake with 6 and traditional running speed analysis with 8 studies for physiological and methodological validation, respectively. The best-evidence synthesis showed conflicting to strong and moderate to strong evidence for physiological and methodological validity of the approach, respectively. The conceptual studies revealed several modifications regarding the approach that need to be considered. Otherwise, incorrect implementation can occur.

Conclusions

Evidence of the physiological validity of the metabolic power approach ranged from conflicting to strong. However, this should be treated with caution as the validation studies were often partially implemented incorrectly as shown by the underlying concept studies. Moreover, strong evidence indicated that the approach is valid from a methodological perspective. Future studies must consider what the metabolic power approach can and cannot actually display.

A lack of research exists in studies concerning children, females, and team and racquet sports besides soccer and the application of more profound physiological approaches for the validation and assessment of metabolic power estimated by acceleration and speed data is needed.

Previous physiological validation studies are outdated as there have been adaptations concerning the metabolic power approach for estimating metabolic loads over recent years, and methodological validation studies revealing its superiority over the traditional running speed approach.

Distinction between walking and running, different terrains, as well as aerobic and anaerobic energy supply should be considered when assessing metabolic power in team and racquet sports.

Small-Sided Soccer Games with Larger Relative Areas Result in Higher Physical and Physiological Responses: a Systematic and Meta-Analytical Review

This study aimed to systematically review the influence of the relative area on athletes' physical and physiological responses (outcomes) during small-sided games of soccer which were not matched to the relative area. It also presents a meta-analysis comparing standard small-sided games protocols with different relative areas. We searched the Web of Science and Scopus electronic databases for literature published up to March 2020 following all PRISMA guidelines for selecting articles for a qualitative and quantitative synthesis. As a result, eleven articles matched the inclusion criteria. For the quantitative synthesis, a pooled random-effects model was used to make pairwise comparisons between protocols with larger or smaller areas in each selected study. Prediction intervals were used to assess the heterogeneity. We found positive effects of larger relative areas per player on their total distance (d = 0.73; 95% CI = 0.12-1.34; p = 0.006; medium to large effect), distance covered at high speed (d = 0.93; 95% CI = 0.22-1.65; p = 0.001; large effect), and mean heart rate (d = 0.52; 95% CI = 0.17-0.88; p = 0.008; medium effect). In other words, larger relative areas were found to induce higher physical and physiological responses in players. Future studies should consider the relative area per player when comparing data for different small-sided games configurations to avoid confounding variables. Also, coaches can use relative area per player calculations to easily predict increases and decreases in expected training loads for different versions of SSGs during training.

Training Load in Different Age Category Soccer Players and Relationship to Different Pitch Size Small-Sided Games

This study sought to evaluate the training load in different age category soccer players associated with distinct pitch size small-sided games (SSGs). Twenty-four soccer players (eight in each age category: U-12, U-15, and U-23) performed three consecutive 4 vs. 4 ball possession SSGs (SSG1: 16 × 24 m; SSG2: 20 × 30 m; and SSG3: 24 × 36 m) all with 3 min duration and 3 min rest. Subjects carried ultra-wideband-based position-tracking system devices (WIMU PRO, RealTrack System). Total distance covered increased from SSG1 to SSG3 in all age categories and predominantly in running speeds below 12 km·h⁻¹. Moreover, distance covered in 12–18 km·h⁻¹ running speed was different in all performed SSGs and age categories. Residual or null values were observed at 18–21 km·h⁻¹ or above running speed, namely in U-12, the only age category where metabolic power and high metabolic load distance differences occurred throughout the performed SSGs. Edwards’ TRIMP differences between age categories was only observed in SSG2 (U-12 < U-15). The design of SSGs must consider that the training load of the players differs according to their age category and metabolic assessment should be considered in parallel to external load evaluation in SSGs. Wearable technology represents a fundamental support in soccer.