Submaximal Fitness Tests in Team Sports: A Theoretical Framework for Evaluating Physiological State

Team-sports staff often administer non-exhaustive exercise assessments with a view to evaluating physiological state, to inform decision making on athlete management (e.g., future training or recovery). Submaximal fitness tests have become prominent in team-sports settings for observing responses to a standardized physical stimulus, likely because of their time-efficient nature, relative ease of administration, and physiological rationale. It is evident, however, that many variations of submaximal fitness test characteristics, response measures, and monitoring purposes exist. The aim of this scoping review is to provide a theoretical framework of submaximal fitness tests and a detailed summary of their use as proxy indicators of training effects in team sports. Using a review of the literature stemming from a systematic search strategy, we identified five distinct submaximal fitness test protocols characterized in their combinations of exercise regimen (continuous or intermittent) and the progression of exercise intensity (fixed, incremental, or variable). Heart rate-derived indices were the most studied outcome measures in submaximal fitness tests and included exercise (exercise heart rate) and recovery (heart rate recovery and vagal-related heart rate variability) responses. Despite the disparity between studies, these measures appear more relevant to detect positive chronic endurance-oriented training effects, whereas their role in detecting negative transient effects associated with variations in autonomic nervous system function is not yet clear. Subjective outcome measures such as ratings of perceived exertion were less common in team sports, but their potential utility when collected alongside objective measures (e.g., exercise heart rate) has been advocated. Mechanical outcome measures either included global positioning system-derived locomotor outputs such as distance covered, primarily during standardized training drills (e.g., small-sided games) to monitor exercise performance, or responses derived from inertial measurement units to make inferences about lower limb neuromuscular function. Whilst there is an emerging interest regarding the utility of these mechanical measures, their measurement properties and underpinning mechanisms are yet to be fully established. Here, we provide a deeper synthesis of the available literature, culminating with evidence-based practical recommendations and directions for future research. Supplementary Information The online version contains supplementary material available at 10.1007/s40279-022-01712-0.


Research Questions
The methodology component of our review was executed in accordance with PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [1]. We defined our research questions by the PICOS model [1]: Population Team-sports athletes (refer to criteria 4 of the inclusion-exclusion criteria; Table 2).
Intervention (exposure) 1) No exposure, 2) Exposure to acute, short-term or chronic training regimen, 3) Exposure to extreme environments (heat, altitude). 4) Training interventions integrated into the general program such as high-intensity interval training.

Outcomes
Athlete's cardiorespiratory/metabolic, subjective, mechanical measures or any combination of which collected during or soon after SMFT.

Study design
We accepted any: a) test-retest or correlational study designs: b) observational with single/repeated measures designs with or without reporting training loads, training context or environment; and c) training intervention studies that incorporated pre and post measurements.

Search Strategy
The electronic databases MEDLINE, Scopus, and Web of Science were used at multiple occasions (started on January 23rd, 2020, and finalised on August, 2021), including two independent searching strategies and combination of relevant free text terms linked to the Boolean operator 'OR' (levels). The final search was created by merging all term levels using the 'AND' operator ( Table 1). The search syntaxes of the searching strategy are presented in Table 3. Further searches of the relevant literature were also conducted using other databases and reference lists. Level 6 athletes OR players OR "team sport" OR "team sports" OR "team based sport"

Screening Study and Selection
To select the appropriate articles, the first author (TS) initially exported the electronic search results to the reference management software Endnote (version X9), and then to a Microsoft Excel spreadsheet for further evaluation (N = 2170 records). Duplicates records were identified and removed (N = 1155), and an assessment of the remaining studies was undertaken according to the inclusion-exclusion criteria, in a sequential manner (i.e., criteria 1-8; Table 2). Consequently, more studies (title; N = 672 and abstract; N = 255) were discarded, and overall 107 full text studies were reviewed.

Data Extraction and Analysis
The following data were independently extracted from each eligible study: 1) player  Studies examining the validity of SMFT outcome measures and reporting correlational statistic of the relationships between SMFT outcome measure and a criterion measure(s) (for example, the relationship between SMFT exercise heart rate and aerobic capacity test scores). Observation with single/repeated measures Including studies where usual training process was monitored and administered SMFT to infer athlete's physiological state (e.g., discriminate between individuals or evaluate training effects within individuals). Training interventions with pre-and post-measurements Including experimental trails where usual training process was coupled with an experimental intervention (e.g., highintensity interval training) and SMFT were administered to infer athlete's training effects.
6 Settings SMFT were administered either in laboratory, indoor/outdoor field formats or combination of two.

SMFT
Any SMFT including cycling, running, specific drills or games (refer to section 3.2 in the text: SMFT protocol taxonomy)

Intensity
The intensity was non-exhausting (refer to section 3.1 in the text: SMFT definition)

Duration
The duration was ≤15 minutes of exercise for all SMFT, while exercise refers to the time when the outcome measures were monitored. Therefore, the duration of rest intervals during specific test protocols (e.g., recovery between sets during X bouts of incremental test or small-sided games) were not considered in the total duration, regardless if any outcome measure (e.g., heart rate recovery) was collected during this time.

Outcomes Measures
Cardiorespiratory/metabolic, subjective and/or mechanical SMFT submaximal fitness tests