Introduction

Definitions and Framework of Cumulative Load in Football

• Definition of Cumulative Load: According to the literature, cumulative load is most commonly defined as the total amount of physical and physiological stress experienced by football players over a specific period, typically a week. This stress is measured using various variables, different metrics, and diverse monitoring methods (Zuru Tusa; Castel Salano Castelano, 2017).
• Alternative Definitions: Other studies define cumulative load through the cumulative effect of external load metrics. Specifically, it refers to the ongoing impact of variables such as acceleration and deceleration during a soccer match.
• Impact on Neuromuscular Performance: Cumulative load affects neuromuscular fatigue by impacting muscle function and general player performance. This is particularly evident in specific movements such as countermovement jumps (CMJ) and sprinting.
• Predictive Value: The quantification of percentage changes in external load metrics provides a useful, non-invasive predictor of the subsequent neuromuscular fatigue status in soccer players immediately following a match.
• Mechanical Load and Muscle Specificity: Cumulative load is closely related to mechanical load, particularly the number of changes of direction (COD). These movements affect muscles differently:
  • Quadriceps: Increasing the coordination of changes of direction is found to increase fatigue in the quadriceps.
  • Hamstrings: The hamstrings are less likely to experience the same levels of fatigue as the quadriceps during these mechanical changes.
• Correlation with Fatigue: Research indicates significant correlations between accumulated load and neuromuscular fatigue; higher total loads are consistently associated with higher fatigue levels.
• Normalization of Demands: Normalizing training demands relative to competition helps individualize player training loads. This process is essential for managing fatigue and optimizing overall performance.
• Progressive Declines: Neuromuscular fatigue contributes to progressive declines in performance, specifically in CMJ and hamstring strength. However, there is a conflict in the literature regarding these findings, with some opposing views being documented.
• High-Intensity Training Effects: While direct correlations between individual session loads and impairments are not always found, the timing and cumulative effect of high-intensity training—specifically eccentric loads from decelerations—play a significant role in neuromuscular decline.

Fixture Congestion, Injury Risk, and Performance

• Fixture Congestion: Cumulative load is also defined by the effect of repeated matches without adequate recovery time. This leads to increased mental and physical fatigue, compromised performance, and increased injury risk due to the accumulation of central and peripheral fatigue (Thomas Dent, Howe, Watson, 2017).
• Gender-Specific Research Context: Fixture congestion is noted as an issue specifically affecting university female football teams, putting players at significant risk due to limited recovery windows.
• Explosive Performance and Dynamic Balance: The effect of football-specific fatigue on explosive neuromuscular performance and dynamic balance is under-researched despite its implications for injury. Fatigue reduces maximal voluntary torque in knee flexors and extensors but does not necessarily affect explosive torque.
• Balance Response: Fatigue impairs the balance response, specifically regarding posterior perturbations, which is linked to an increase in injury risk. Research indicates that impaired balance response, rather than changes in explosive torque or muscle balance ratios, is the key factor in injury risk due to the influence of fatigue on sensory and proprioceptive processes (Behan, Willis, Payne, Foland, 2018).
• Injury Timing: The majority of football injuries occur in the latter part of games, indicating that fatigue is a causative factor.
• Fatigue Dimensions: Research addresses the complex nature of fatigue by examining multiple dimensions: physical, physiological, neuromuscular, and metabolic. Comprehensive fatigue management strategies are necessary to reduce injury risk (Kerber, Jamora, Moses, 2026).
• Gender Bias in Research: There is a consensus that existing research is dominated by male participants (elite, semi-professional, and youth), resulting in very limited data for female footballers.
• Specific Recovery Timelines:
  • Immediate Post-Exercise: Central fatigue is prominent immediately after exercise and remains depressed at $48\,\text{hours}$.
  • Peripheral Fatigue: Declines by $14\%$ post-exercise and may not be fully recovered by $72\,\text{hours}$.
  • Injury Rates: Playing two matches per week can increase injury rates six-fold compared to playing only one match per week. Short intervals (e.g., $24\,\text{hours}$) drastically increase risk compared to longer intervals (Thomas Dent, Howatson, Goodall, 2017).
• Leg Stiffness: Soccer-specific fatigue leads to decreased leg stiffness, which increases the risk of lower limb injuries due to reduced dynamic knee stabilization.
• Reactive Strength Index: Despite fatigue, reactive strength index may increase, indicating an enhanced ability to transition from eccentric to concentric contractions. This suggests that fatigue may not always compromise muscle control or isokinetic strength (Lee, Linnert, Croix, Xavier Auve, Botek, 2018).

Monitoring Methods: The Countermovement Jump (CMJ)

• Overview: The CMJ is a widely utilized neuromuscular monitoring method in soccer, though its effectiveness is dependent on target metrics and data interpretation (Mark Dojaj, Kasa, 2025).
• Reliability Data: In youth soccer players, $15$ out of $25$ CMJ metrics demonstrate acceptable reliability, defined as a coefficient of variation $CV \ge 10\%$ and an intraclass correlation $ICC \ge 0.75$ (Andrew J. Badby et al., 2025).
• Sensitive Metrics: Mean propulsive force, velocity, power, and jump momentum are sensitive to acute post-match changes in players.
• Meta-Analysis Findings: A meta-analysis of $151$ articles and $531$ effect sizes showed that average CMJ height is more sensitive than peak jump height for detecting fatigue (Claudino et al., 2017).
• Metabolic Stress: CMJ is highly correlated with blood lactate and ammonia concentrations, making it useful for estimating metabolic stress. However, it may not capture performance aspects unrelated to metabolic or neuromuscular stress (Morcillo et al., 2015).
• Predictive Limitations: While CMJ detects post-match fatigue, it has been found not to predict subsequent match output. Wellness measures are often better predictors of future performance (Evans et al., 2021).
• Body Weight Considerations: Standard CMJ approaches may overlook mechanical changes; body weight changes must be monitored simultaneously with mass-related metrics (Badby et al., 2026).

Wellness and Subjective Monitoring

• Questionnaires: Tools like the Hooper Index and Total Quality Recovery (TQR) scale are sensitive to training loads and can detect early signs of fatigue (Selmi et al., 2022).
• Sensitivity to Loading: Analysis of $2,583$ questionnaires from $27$ players over $183$ days showed wellness ratings are sensitive to weekly training manipulations and unloading periods (Gaston et al., 2013).
• Barriers to Effectiveness: A survey of $41$ professional clubs found a $23\%$ gap between expected and actual effectiveness of monitoring for injury prevention. Primary barriers include limited human resources and poor coach buy-in (Ackinhead and Nasis, 2016).
• Isolated vs. Integrated Monitoring: A review of $46$ studies identified a trend of fragmented monitoring, lacking integration between physical, psychological, and technical domains (Pedro Afonso et al., 2025).
• Internal vs. External Load components:
  • Internal Load: Measures like Rating of Perceived Exertion (RPE) and heart rate.
  • External Load: Measures like running and accelerometry.
• Wellness Components: Include sleep quality, muscle soreness, stress, and mood. Poor sleep quality negatively impacts performance and increases injury risk, while high sleep quality improves emotional and physical well-being (Oliver Girard, 2025).
• Biomarkers vs. Subjective Measures: Objective measures (heart rate) cannot inform on all aspects of wellness. Use of daily training logs and psychometric tests combined with performance tests (CMJ) is advised for a complete solution (Buchheit, 2014).

GPS Technology and External Load Metrics

• GPS Prevalence: GPS is one of the most widely used monitoring methods in professional football to track acceleration, total distance, and high-speed running (Western, 2018; Ackinhead and Nasis, 2016).
• Underreporting Issues: GPS system can provide significantly underreported distances at higher velocities (up to $39\%$) compared to motion camera tracking systems (Dalloway, 2014).
• Real-Time Application: A benefit of GPS is the ability to transmit data in real-time, allowing for interventions before the onset of fatigue (Feletti et al., 2019).
• Effectiveness Discrepancy: While widely used, there is a $23\%$ discrepancy for injury prevention and $20\%$ for performance enhancement between expected and actual outcomes (Ackinhead and Nasis, 2016).
• Standardization Needs: There is a lack of standardized intensity thresholds for acceleration and deceleration, leading to a predominance of low-intensity efforts in training compared to competition (Silva et al., 2022).

Muscle Fatigue Mechanisms and Force Relationships

• Physiological Mechanisms: Soccer fatigue involves changes in maximal force, shortening velocity, and the curvature of the force-velocity relationship.
• Glycogen Depletion: Reduced muscle glycogen depletion is a key factor in the latter stages of a game. Low glycogen in muscle fibers impairs excitation-contraction coupling, including action potential propagation, calcium handling, and cross-bridge cycling through reductions in muscle ATP.
• Acceleration and Deceleration Costs: Accelerations have a higher metabolic cost. Decelerations have a higher mechanical/metabolic load that inflicts greater damage on soft tissues, especially if high force impacts are not attenuated (Marquez et al., 2022).
• Performance Metrics Correlation:
  • Change in $10\,\text{m}$ sprint time is largely correlated with internal loads.
  • Change in $20\,\text{m}$ sprint performance can be predicted accurately using changes in acceleration and deceleration.
  • Internal load metrics (heart rate max percentage and time at $90\text{-}100\%$ HR max) correlate with changes in $10\,\text{m}$ sprint efficiency ($r = 0.636$, $p = 0.48$; $r = 0.6$, $p = 0.038$).
  • CMJ height change is linked to high-intensity decelerations and accelerations ($r = 0.689$, $p = 0.027$).

The Isometric Mid-Thigh Pull (IMTP)

• Overview: IMTP is a multi-joint test measuring maximum force generation in a static isometric contraction (Comfort et al., 2019).
• Protocols Compared:
  • Traditional Protocol: $3\text{-}5\,\text{second}$ maximal force production, $2\text{-}3\,\text{minute}$ rest.
  • Short Protocol: $1\,\text{second}$ maximal force production, $30\,\text{seconds}$ rest (Guppy et al., 2022; Suarez et al., 2022).
• Comparative Results:
  • No significant difference in peak force ($p = 0.345$, $g = 0.07$).
  • Early force-time variables significantly higher in the short protocol ($p < 0.001$).
  • Short protocol is more reliable for Rate of Force Development (RFD) measures within a session, with an $ICC$ of $0.97\text{-}0.99$ and $CV$ of $2.6\text{-}7\%$.
  • The traditional protocol results in a significantly higher $CV$ of $14.1\text{-}38.5\%$ for early force measures.
• Time-Effective Monitoring: The short protocol is a time-effective alternative for assessing both peak and early force generating capacity (Stephens, Currey, Gaston, James, 2025).
• Joint Angles: Reliability is high regardless of posture, though specifically noted at $113^{\circ}$ knee flexion and $125^{\circ}$ hip flexion.
• Sensitivity to Training Decay: IMTP impulse to $250\,\text{ms}$ decreases significantly from baseline to $48\,\text{hours}$ post-resistance training ($p = 0.046$, $dB = 0.88$), making it a viable tool to monitor performance changes up to $48\,\text{hours}$ after training (Ashida, Basile, Suarez, 2023).

Research Study Aims and Hypothesis

• Scientific Gap: There is an absence of a widely accepted fatigue measure for female soccer. Current literature is based on homogeneous male samples.
• Study Aim: To determine whether the short IMTP protocol and single acceleration/deceleration metrics (across $10\text{-}20\,\text{m}$) can be used as a fatigue monitoring tool for recreational-level female football athletes.
• Hypotheses:
  • Players will show a significant decrease in peak force, acceleration, and deceleration over consecutive testing weeks.
  • Determine the relationship between changes in short IMTP metrics and changes in sprint metrics over a five-week testing period.
  • Players with higher combined match exposure will exhibit greater neuromuscular fatigue and worse wellness scores.
  • Determine if players with higher load volume and wellness scores demonstrate a significant increase in neuromuscular fatigue or change.