Countermovement Jump and Quantitative Electroencephalography Assessment in Division I Football Athletes: An Exploratory Neurophysiological Study of Return‑to‑Play Readiness

INTRODUCTION

Force-plate technology has become integral in neuromuscular assessment in both rehabilitation and performance contexts because of its ability to quantify lower-limb asymmetries, tendon stiffness, neuromuscular power, and jump strategies.^1,2 The countermovement jump (CMJ) is widely used to assess functional mechanics, explosive strength, and readiness during rehabilitation, providing sensitive measures of vertical power and reactive strength.³ Mechanical metrics alone often make it challenging to determine whether observed deficits stem primarily from peripheral musculoskeletal impairment, central nervous system (CNS) dysregulation, or a combination of both. Consequently, there is increasing interest in complementary assessments that provide insight into cortical activation and neurophysiological status alongside lower-limb biomechanics.

Over the past decade, clinical hop testing has evolved^4,5 to include comprehensive force-plate–based functional profiling that provides objective and standardized outcomes to monitor lower-extremity progressions associated with return-to-play (RTP).^6–8 Within this framework, CMJ-derived variables—such as jump height, reactive strength index–modified (RSI-Mod), and concentric/eccentric force output—help identify compensatory strategies and latent performance limitations that may have implications for RTP readiness.^3,6

Quantitative electroencephalography (qEEG) has emerged as a complementary method for detecting cortical activity changes following musculoskeletal injury. Prior research indicates that ACL and other lower-extremity injuries may be associated with alterations in cortical activation and functional connectivity, which could contribute to persistent motor-control differences even after conventional musculoskeletal criteria have been achieved.^9–12 These neurophysiological adaptations have been described even in clinically cleared athletes following ACL injury, where altered cortical activation, disrupted sensorimotor integration, and hemispheric imbalance have been reported.¹³

In parallel, functional neuroimaging and electrophysiological studies suggest that disrupted afferent–efferent integration and interhemispheric balance within motor-planning regions may persist during dynamic tasks, even when clinical measures of musculoskeletal recovery appear restored.^6,14 Collectively, these findings suggest that CNS contributions to ongoing functional deficits are plausible, although specific mechanisms remain incompletely understood.

Traditional RTP testing typically emphasizes peripheral measures such as muscle strength, hop performance, and visual assessment of movement quality. Although these variables are essential, they may not fully capture potential contributions from the CNS—for example, altered cortical activation, sensorimotor integration, or attentional demands during high-speed tasks. Integrating force-plate CMJ metrics, movement-quality assessment, and neurophysiological measures such as qEEG may offer a more complete view of how brain and body interact during sport-relevant movements in athletes recovering from lower-extremity injury.¹⁵

The purpose of the study was to explore neuromechanical, movement-quality, and cortical activation patterns during countermovement jump performance in previously injured and non-injured Division I football athletes using an integrated force-plate, functional movement, and qEEG assessment approach.

METHODS

Participants: Ten male NCAA Division I football athletes participated: five previously injured and five healthy controls. The injured group included heterogeneous lower-extremity conditions—ACL tear, Achilles Rupture, hamstring strain, meniscus repair, and midfoot injury.

All injured athletes were medically cleared by the team’s sports medicine staff in accordance with institutional RTP criteria. Clearance typically requires: (1) restoration of joint range of motion; (2) successful performance of functional hop and/or plyometric tasks; (3) absence of joint effusion; (4) stable imaging findings and/or surgical clearance when applicable; and (5) tolerance of unrestricted football practice. Control athletes had no history of lower-extremity injury. Participants were matched by height, weight, and sport, and were further grouped using the Skill, Big, and Big Skill positional demand classification framework that has been used in prior CMJ and performance studies to distinguish neuromuscular and loading demands across roles¹⁶ (Table 1).

Procedures Overview: All athletes completed the Neuralytica qEEG (Neuralytica, Los Angeles, California) neuromuscular and cognitive-motor assessment battery, followed by standardized CMJ testing on force-plates with synchronized qEEG acquisition. The Neuralytica battery, previously described in Division I athletes,¹⁷ comprises task-based evaluations of cognitive control (e.g., Stroop task), reaction time, motor imagery, sustained attention, task load, stress response, and functional single-leg and bilateral movement performance. All assessments were conducted within a single session for each athlete under standardized environmental and procedural conditions.

Countermovement Jump Testing

Equipment and Setup: CMJ performance was assessed using VALD ForceDecks™ (VALD Performance, Brisbane, Australia) dual force platforms sampling at approximately 1,000 Hz. Manufacturer-validated algorithms were used to derive reactive strength index–modified (RSI-Mod), jump height, impulse, and landing force variables, with automated detection of movement onset, takeoff, and landing. Testing was conducted indoors on a standardized performance surface, and athletes wore their customary training footwear.

Protocol: Consistent with widely used VALD CMJ protocols, athletes:

1. Stood still for ≥2 seconds to establish baseline force.

2. Performed CMJs with hands on hips (no arm swing) to reduce upper body strategy variability and improve signal clarity for synchronized qEEG.

3. Completed three maximal effort trials, each separated by 60 second rest intervals to reduce fatigue carryover and support qEEG stability.

CMJ movement strategy variability (e.g., hip- versus knee-dominant mechanics) was not constrained, as the study sought to capture athletes’ natural movement patterns. A hands-on-hips constraint was applied to standardize upper-extremity contribution, thereby providing a consistent boundary condition for comparison of kinetic and cortical measures across participants.

CMJ Outcomes: Predefined primary mechanical variables were:

• RSI-Mod (unitless): jump height ÷ time to takeoff, indexing stretch shortening cycle efficiency.

• Jump height (cm): calculated from the force–time signal.

• Peak landing force (N): peak vertical ground reaction force at landing.

Secondary exploratory variables included:

• Concentric impulse (N·s).

• Force at zero impulse (N), representing a surrogate measure of preload/stiffness at the braking–propulsion transition.

For each variable, the mean of three valid trials was used for analysis.

Neurophysiological Assessment (qEEG)

Acquisition: qEEG data were acquired using a 19-channel system configured according to the international 10–20 electrode placement standard prescribed by Neuralytica. Signals were recorded via a wireless amplifier at a sampling rate of 500 Hz. Electrodes were positioned over frontal, central, parietal, and occipital regions and secured via a dry-electrode cap. Prior to testing, electrode impedance and signal quality were verified using manufacturer-provided indicators, and adjustments were made until acceptable impedance thresholds were achieved. Continuous EEG data were band-pass filtered (0.5–45 Hz), and a 60 Hz notch filter was applied to minimize electrical line noise.

Synchronization With CMJ: Each CMJ trial was initiated using a standardized visual stimulus. Computerized digital trigger markers were used to synchronize qEEG recordings with key kinetic events: CMJ onset, eccentric and concentric phases, and landing. This synchronization enabled precise temporal alignment of cortical activity with corresponding biomechanical events.

Preprocessing and Quality Control: Preprocessing procedures were conducted in accordance with standardized sports neuroscience protocols consistent with Neuralytica baseline methods. Following acquisition, data underwent automated and manual quality control procedures. Visual inspection was performed to identify non-physiological artifacts (e.g., cable displacement, amplifier saturation). Independent component analysis was applied as needed to isolate and remove components primarily associated with ocular activity and movement-related electromyographic artifact.

Persistently noisy channels were removed or interpolated using neighboring electrode data. Data segments that did not meet predefined artifact-free criteria were excluded from analysis. These procedures were implemented to ensure that derived qEEG metrics reflected physiological neural activity with minimal contamination from environmental or motion-related artifacts.

qEEG Outcomes: Predefined primary qEEG outcomes were:

• Sensorimotor Rhythm (SMR) (12–15 Hz) power at C3 and C4.

• SMR asymmetry index (z score normalized relative to a normative athlete database).

Exploratory qEEG outcomes included:

• Reaction time (left/right sides)

• Reaction time asymmetry (%)

• Stroop accuracy (%)

• Cognitive workload

• Sustained attention

• Performance under pressure

Exploratory metrics were derived from raw EEG signals recorded during the administration of the Stroop test and a computerized reaction time task. Behavioral outcomes included manual reaction time (measured in milliseconds for stimuli presented in the left and right visual fields), reaction time asymmetry (percentage difference between fields), and Stroop accuracy (percentage of correct responses).

Cognitive load, sustained attention, and performance under pressure were calculated as proprietary indices via Neuralytica software. These metrics utilize algorithmic transformations of raw EEG power spectra—specifically involving SMR asymmetry and three-dimensional cortical connectivity—to estimate psychomotor efficiency and CNS precision.^18,19 Specifically:

• Cognitive Workload: A unitless index representing the estimated depletion of mental resources and the degree of sensory-cognitive demand placed on the brain.¹⁸

• Sustained Attention: A metric derived from the ratio of specific frequency bands (e.g., theta/beta or SMR) reflecting the maintenance of CNS arousal and sensory processing.¹⁹

• Stroop Test: A neuropsychological assessment used to measure cognitive interference and inhibitory control; performance requires the integration of selective attention and executive suppression of simultaneous stimuli.^20,21

Functional Movement Assessment

Functional movement assessment (FMA) quality was evaluated concurrently with CMJ testing using video-based observation. Certified athletic trainers, trained in standardized functional movement assessment frameworks, reviewed movement patterns during tasks relevant to lower-extremity control, including:

• Single leg lunge and single, standard-step, step-down mechanics.

• Landing alignment and trunk control during the CMJ.

• Pelvic stability and knee over foot positioning during qEEG neuromuscular battery.

• Symmetry of limb loading during all tasks.

• Presence or absence of visible compensatory strategies (e.g., hip shift, trunk lean).

Video analysis was conducted following testing and focused on qualitative assessment of movement strategy rather than quantitative scoring. The objective was to characterize observable asymmetries, motor control deficits, or compensatory patterns that may not be fully captured by force-plate metrics alone.

Functional asymmetry was descriptively defined by the same athletic trainers who analyzed the tasks based on visible inter-limb differences during single-leg and transitional tasks. Inter-limb asymmetry ranges (e.g., ≤5% or ≥10–15%) were referenced contextually from performance literature and were not applied as validated diagnostic thresholds. These qualitative observations were used to complement CMJ and qEEG findings and to contextualize neuromechanical and neurophysiological outputs within the broader movement profile of each athlete.

Data Processing

Force-Plate Data: Kinetic variables were normalized to body mass where appropriate. Inter-limb asymmetry was calculated as the percentage difference between dominant and non-dominant limbs. For each participant, the mean of three valid CMJ trials was used for group-level analyses. All CMJ variables were derived from the force–time curve using manufacturer-provided VALD ForceDecks™ algorithms.

qEEG Data: SMR asymmetry was calculated using z-score normalization relative to a normative athlete reference database and expressed as the relative difference in activity between left and right motor cortices. EEG features were extracted from electrodes in motor-related regions of interest, including C3, C4, and adjacent parietal locations.

Indices reflecting workload and sustained attention were generated using standardized Neuralytica analytic algorithms applied to the processed EEG signal. Physiometric signals, including heart rate, heart rate variability, respiration, electromyography, and galvanic skin response, were collected as part of the broader research protocol; however, these variables were not analyzed for the present study and are not reported here.

RESULTS

Participant Characteristics

Ten NCAA Division I football athletes (5 previously injured, 5 healthy controls) participated in the study. Participants were categorized by recruiting classification to reduce positional variability within the small sample size: Skill (n=4), Big (n=4), and Big Skill (n=2) groups were balanced between cohorts (Table 2). Injured athletes were, on average, older than controls (22.0 vs 19.2 years). The injured cohort was an average of 5 months and 2 weeks post-injury, with injuries ranging from ligamentous tears to muscle strains; all had been medically cleared for full return-to-sport (Table 3).

Neuromuscular and Cognitive Performance

Group-level comparisons demonstrated descriptive differences in CMJ and cognitive–motor performance between injured and non-injured athletes (Table 4). Previously injured athletes exhibited lower RSI-Mod, reduced jump height, and lower peak landing forces, accompanied by modestly slower reaction times and slightly greater reaction-time asymmetry. Stroop accuracy was comparable between groups. Qualitative movement assessment indicated greater single-leg asymmetry and reduced step-down control in the injured cohort.

Neurophysiological measures demonstrated slightly prolonged left- and right-sided reaction times and marginally greater inter-limb reaction-time asymmetry among injured athletes, while Stroop interference accuracy remained similar between groups (Table 5). Cognitive-load and attention-related indices derived from the proprietary neurocognitive module indicated lower sustained attention, higher perceived workload, and reduced performance consistency under task demands in the injured group (Table 6). These metrics represent exploratory, system-generated descriptors and do not constitute validated psychometric measures.

Functional Movement and Cortical Asymmetry

Functional movement analysis revealed qualitatively reduced dynamic control during single-leg tasks and greater observable inter-limb asymmetry in the injured cohort (Table 7). Injured athletes also demonstrated higher SMR asymmetry across motor-related cortical regions based on exploratory qEEG metrics.

Contextual Comparison to RTP Benchmarks

When compared with commonly cited RTP reference values, injured athletes demonstrated performance below typical ≥90% benchmarks for RSI-Mod and jump height, with smaller relative differences observed for landing force and reaction time (Table 8). These benchmarks are heuristic reference values drawn from prior literature and are presented for contextual comparison only.

DISCUSSION

This exploratory cross-sectional study examined neuromuscular and neurophysiological characteristics during CMJ performance in previously injured and non-injured Division I football athletes. Although all injured athletes had been medically cleared for RTP, those with prior injury demonstrated lower RSI-Mod and jump height values, reduced peak landing forces, modestly slower reaction time measures, and more frequent qualitative movement asymmetries. qEEG-derived SMR measures also suggest greater interhemispheric asymmetry within motor-related cortical regions among previously injured athletes compared to controls.

Given the small sample size and cross-sectional design, these findings should be interpreted as descriptive rather than inferential. However, the observed patterns are consistent with prior literature indicating that lower-extremity injury may be associated with persistent functional alterations beyond the point of clinical clearance and that such alterations may involve central neuromuscular processes in addition to local musculoskeletal factors.^1–3,9,14

The current findings are consistent with emerging literature on the neurophysiology of ACL and lower-extremity injury, which suggests that ligament trauma involves more than structural disruption and may include central and peripheral nervous system alterations affecting sensorimotor integration and neuromuscular control.^11,13,22 Prior work indicates that injury-related changes in cortical excitability, functional connectivity, and motor planning regions may contribute to persistent movement deficits, even after conventional clinical and strength criteria have been achieved.^{1–3,9,13,14} Within this context, the observed neuromuscular differences (e.g., lower RSI-Mod, altered landing forces, and movement asymmetries) and concurrent SMR asymmetry may reflect coexisting peripheral and central adaptations following injury. This integrated, real-time assessment approach - combining CMJ force-plate metrics, qualitative movement observation, and exploratory qEEG measures - offers a framework for examining how these adaptations may co-express during a sport-relevant task.

The integration of CMJ force-plate metrics, qualitative functional movement assessment, and qEEG measures was feasible within a collegiate performance environment and may provide a more comprehensive characterization of neuromechanical status than single-domain assessments alone. In this sample, lower RSI-Mod and jump height values observed in previously injured athletes are consistent with reduced explosive neuromuscular performance, whereas lower peak landing forces may reflect an altered impact-absorption strategy. These mechanical findings corresponded with greater observable movement asymmetries and increased SMR asymmetry within motor-related cortical regions. Collectively, these patterns may suggest persistent adaptations following injury, although causal relationships cannot be established within the present design.

CMJ performance requires coordinated integration of afferent sensory input and efferent motor output across both musculoskeletal and central neural pathways. Prior neurophysiological research suggests that lower-extremity injury may be associated with changes in cortical excitability, sensory integration, and interhemispheric balance; however, the present study design does not allow determination of specific underlying mechanisms.^8,14,15,23 A review by Stanczak et al. emphasizes that ACL injury affects both central and peripheral pathways, altering sensorimotor integration across the movement system.¹³ Within this broader context, the current observation of elevated SMR asymmetry alongside neuromechanical and movement asymmetries is consistent with a central–peripheral involvement hypothesis: persistent deficits after injury may reflect a combination of peripheral impairments (e.g., strength, mechanics, movement strategy) and central adaptations (e.g., cortical activation or sensorimotor integration).

Multidomain reductions in reactive strength, power, landing mechanics, and reaction time-accompanied by lower sustained attention, higher perceived workload, and reduced performance consistency under task demands-may reflect increased cognitive effort during movement execution.²⁴ These exploratory cognitive-load indicators provide contextual insight into how attentional resources may be allocated during athletic tasks; however, they should be interpreted cautiously given their proprietary derivation and qualitative classification.

From a neurophysiological perspective, qEEG-derived metrics such as SMR asymmetry offer a noninvasive measure of cortical involvement during motor performance. Greater asymmetry may reflect increased reliance on cortical control processes rather than more automatic motor patterning. This aligns with the psychomotor efficiency hypothesis, which posits that higher SMR activity is associated with superior performance and reduced task-irrelevant cortical interference, suggesting that the observed asymmetry in the injured cohort may represent a compensatory shift toward less efficient, conscious control.²⁵ Though this interpretation remains hypothesis-generating within the present study design, it provides a neurophysiological basis for the observed mechanical and movement deficits. Notably, central dysregulation after lower-extremity injury is not exclusive to ACL pathology; similar brain–body connectivity disturbances have been reported in patients after Achilles rupture and meniscal injury, though these groups remain underrepresented in neurophysiological studies.^10,11,26 In this sense, multimodal assessment is less about diagnosing a specific lesion and more about characterizing how an individual’s brain and body reorganize to meet task demands.

Traditional RTP models primarily emphasize restoration of musculoskeletal function, including strength, range of motion, pain resolution, and, in some cases, hop or jump symmetry. The persistence of delayed neuromuscular timing, inter-limb asymmetry, altered landing strategies, and reduced attentional performance under task demands in the previously injured cohort highlights the potential value of incorporating neurophysiological assessment to detect subtle deficits not captured by biomechanical measures alone.

From a neurophysiological perspective-particularly in the context of ACL injury-unrecognized central and peripheral adaptations may contribute to ongoing performance alterations following clinical clearance.^8,11,22 These adaptations can manifest as changes in sensorimotor integration, neuromuscular control, and cortical activation, which may not be detected by standard musculoskeletal assessments.^8,27,28 However, prospective and longitudinal studies are necessary to further clarify these relationships and their implications for return-to-sport decision-making.

Finally, asymmetry and performance reference values (e.g., ≥90% of a baseline, <5% asymmetry) were treated as heuristic reference points rather than validated RTP cutoffs. These benchmarks are widely cited but remain context-dependent and were not validated within the present design.^6,11 Consequently, the current data do not permit inference regarding reinjury risk or the effectiveness of specific RTP strategies. However, the findings support further investigation of qEEG-derived metrics as potential adjunctive measures to traditional musculoskeletal benchmarks, particularly in cases where clinical presentation and mechanical performance measures are incongruent.^27,28 Identifying these neural-mechanical discrepancies may eventually facilitate the development of more comprehensive return-to-performance profiles that integrate both physical capacity and neural efficiency.

From a clinical perspective, these exploratory findings suggest that a multimodal assessment approach-including CMJ metrics, qualitative movement evaluation, and qEEG measures, may help identify residual deficits not detected by strength or hop testing alone. Larger longitudinal studies with reinjury tracking, neuromechanical follow-up, and repeated qEEG assessment will be important to determine whether such integrated profiles meaningfully enhance RTP decision-making or inform the development of targeted neurocognitive or neurofeedback-based interventions.

LIMITATIONS

This study has several important limitations. The sample size was small and heterogeneous with respect to injury type, surgical status, age, playing position, and time since injury, introducing substantial between-subject variability and limiting generalizability. Although individual characteristics are provided, variation in injury pathology and recovery timelines likely contributed to observed differences in neuromechanical and neurophysiological measures.

The cross-sectional design further limits interpretation. Analyses are descriptive and do not include inferential statistical testing or prospective reinjury tracking. Accordingly, findings should be interpreted as preliminary and hypothesis-generating rather than confirmatory.

Several outcomes—including cognitive-load indicators and qEEG-derived variables such as SMR asymmetry—were generated using proprietary analytic platforms. Although established preprocessing, artifact-rejection, and signal quality-control procedures were applied, independent validation and test–retest reliability of these derived indices were not examined within this cohort. These measures should therefore be interpreted descriptively.

Collectively, these limitations reflect the exploratory nature of the investigation and underscore the need for larger, more homogeneous samples, longitudinal designs, prospective injury tracking, and independent validation of neurophysiological and cognitive-motor metrics before consideration for integration into clinical return-to-sport decision-making.

CONCLUSION

Medically cleared Division I football athletes with a history of lower-extremity injury demonstrated concurrent neuromechanical, movement-quality, and neurophysiological differences during CMJ performance compared to non-injured teammates, characterized by lower RSI-Mod and jump height, reduced peak landing forces, greater qualitatively observed movement asymmetries, and higher SMR asymmetry within motor-related cortical regions. These findings support a neurophysiological framework in which lower-extremity injury is associated with persistent alterations in both peripheral mechanical function and central motor control processes. Clinically, this multimodal approach highlights the importance of the brain–body interaction and suggests that qEEG-derived indices may identify subtle residual deficits not detected by isolated musculoskeletal testing. However, given the small, heterogeneous sample and cross-sectional design, larger longitudinal investigations are required to determine how these integrated neurophysiological metrics can meaningfully inform rehabilitation strategies and return-to-sport decision-making.

Conflicts of interest

The authors declare that there are no conflicts of interest regarding the publication of this paper. The authors have no financial or personal relationships that could inappropriately influence their actions or decisions.