Physiological and Biomechanical Monitoring in American Football Players: A Scoping Review

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TL;DR

This scoping review of 112 studies maps biomedical engineering applications in American football, finding that concussion biomechanics is the most researched area, followed by training load monitoring and heat illness prevention. Key findings include that head impacts are predominantly low-severity (median 20.5 g linear acceleration), linemen face higher heat illness risk due to lower self-generated airspeed, and no studies addressed shoulder pad innovation or comprehensive vital sign monitoring. The review identifies critical gaps in internal load monitoring, non-invasive temperature measurement, and wearable sensor validation for footwear and sport-specific movement analysis.

Full summary

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**Background:** American football has high injury rates (5.5 per 1000 exposures in practice, 37.2 per 1000 in games), with concussion rates of 2.9 per 1000 in games and 0.43 per 1000 in practice. Despite extensive research on individual topics, no prior review had systematically mapped biomedical engineering applications across the sport. This scoping review aimed to report on biomedical engineering research in American football, highlighting main topics and challenges.

**Methods:** A systematic literature search was conducted in PubMed, Web of Science, and Scopus following PRISMA and scoping review guidelines. Search terms covered population (American football terms), bioengineering applications (mechanics, monitoring, sensors, wearables), and outcomes (fitness, cardiac, kinematic, performance). The search spanned 1 January 1995 to 20 July 2022. After removing 1629 initial records and screening, 112 studies were included. Exclusion criteria removed studies on retired players, subjects under 18, non-American football sports, finance/economics, diet/nutrition, strength training, and plyometrics. Studies were categorized into: biomechanics of concussion (subcategories: laboratory reconstruction [LAB], head impact telemetry system [HIT], wearable-sensor monitoring [WSM], computer modeling [CM]), biomechanics of foot-wearing (field-footwear interactions [FFI], footwear bending stiffness [FBS]), biomechanics of sport-related movements (SM), aerodynamics of football and catch (AFC), injury prediction (IP), heat monitoring of physiological parameters (HM), and monitoring of training load (TL). Quality of appraisal was assessed using appropriate checklists for each study design.

**Key Results:** The largest research area was concussion biomechanics. LAB studies reconstructed impacts using Hybrid III anthropomorphic test devices, with estimated errors of 7-16% for linear acceleration and 4-25% for rotational acceleration. HIT studies (the largest cohort with 51 concussion cases) reported median peak linear acceleration of 66.7 g and median peak rotational acceleration of 2963 rad/s² for concussive impacts. For sub-concussive impacts, median peak linear acceleration was 20.5 g and median peak rotational acceleration was 1400 rad/s². The median number of season head impacts per player ranged from 257 to 438 across three teams, with median impacts per game of 12.1-16.3 and per practice of 4.8-6.6. The largest cohort (Mccrea et al., n=658) reported a median of 415 head impacts per player per season (IQR 190-727), with most occurring in practice. WSM studies identified s100-beta and neurofilament light chain as blood biomarkers associated with head impact severity. CM studies showed neck muscle strength does not significantly affect injury metrics, but early activation and proper head posture decrease injury risk. For injury prediction, a threshold of 21 touches in the closed-chain upper extremity stability test predicted shoulder injuries with 79% sensitivity and 83% specificity. A 3-factor model (≥1 starting game, Oswestry Disability Index >4, wall-sit hold <88 seconds) predicted core/lower extremity injuries with 56% sensitivity and 80% specificity. Heat monitoring studies found linemen have lower heat loss potential due to lower self-generated airspeed, and the American football uniform reduces heat dissipation, increasing skin temperature and reducing time to reach 40°C. Training load studies showed the first preseason week has the highest workload, and acute-to-chronic workload ratios are associated with injury risk. HRV monitoring revealed linemen experience decreased vagal tone across the season without full recovery between training days.

**Clinical Implications:** The review confirms that concussion is a multidimensional event not solely dependent on impact severity but also on location, frequency, head posture, neck muscle activation, and visual performance, making a universal concussion threshold difficult to define. The finding that most head impacts occur during practice rather than games supports policy interventions to reduce contact practice time. The identification of linemen as a high-risk group for both heat illness (due to lower convective cooling) and parasympathetic impairment (sustained vagal tone reduction across seasons) suggests position-specific monitoring and conditioning protocols are needed. The contradictory results in injury prediction models (e.g., Y-balance test showing 100% sensitivity in one study but no significant differences in another) highlight the need for larger, internally validated studies before clinical implementation. Critical gaps identified include: no studies on shoulder pad innovation, limited internal load monitoring (only 8 of 112 TL studies measured internal load), lack of non-invasive core temperature monitoring solutions, and absence of respiration rate monitoring in real scenarios. Future research should prioritize wearable sensor validation for sport-specific movements, data-driven models for concussion classification, and comprehensive vital sign monitoring during practice and competition.