The Detection of Neural Fatigue during intensive conditioning for football: The Potential of Transcranial Magnetic Stimulation Carl Wells PhD Sport Science Lead, Perform, National Football Centre, St. George s Park
Recovery Status: So What Assessment of Recovery Status = WHY??????? Capability to perform effectively and safely during these intense periods of competition / training / rehab. Definition: An index of the impact frequent exposure to high loads has on an individual s Physiological integrity. Performance Physiological Function
Recovery Status in Football: A Topical Area Club and Country Fixtures Commercial duties: Pre-season / offseason schedules Intensive Conditioning / Rehabilitation
Physical Loads: A Variety HIE Load: Mechanical Locomotive Metabolic Football Physical Loads Competition Load Complimentary Training Loads
Physical Loads: The Bigger Picture HI Distance 2.5 3 km 120 km 3000 Player 1600 Acc/ Decc 300 No. Sprints 50
Physical Loads: The Increasing Demands in the EPL 200 180 160 Number of Activities Performed 140 120 100 80 60 40 2006-2007 2012-2013 20 0 High-Intensity Activities Type of Activity Sprint Number Barnes et al., (2014)
High Physical Load Games / Rehab Condition of Over reaching: Temporal Reduction in performance Sufficient Recovery Reduced Recovery Periods Insufficient Recovery Super-compensation Improved Performance Management of recovery status, performance decrement minimised Condition of Over-training and chromic fatigue
Detecting Recovery Status during Intensive Conditioning
PFA Intensive Rehab Scheme Specific Needs of an Intensive Rehab Scheme Use with players at various stages of rehabilitation Need quick results to ensure injury integrity Non-invasive Player Adherence!!
Key Considerations when assessing Recovery Status 1. Select measures that provide the best data 2. Use this data to individualise recovery strategies
1. Detecting Recovery Status Neuromuscular Function / integrity: Jump Tests Performance tests: Speed, Endurance Physical Output Measures Movement Analysis: GPS Neural Function: Central and Peripheral??? Player Recovery Status Hormonal / Enzyme: Ig, Testosterone Psycho-Physical Process Measures Biological Measures: HRV Wellness Assessment
2. Using Recovery Status Data to Individualise Recovery strategies 5 Recovery Strategy Physical Load - Intensity Classification 4 3 2 Volume: Total Distance Minutes Trained + Played Intensity HI Distance HI Actions Age and injury history 1 0 24 36 48 Recovery Duration (hrs)
2. Using Recovery Status Data to Individualise Recovery strategies Previous strategy is not player specific, more physical output specific! Can we individualise further based on the physiology of the player? Hypothesis: Do highly explosive players who often possess greater proportions of type II muscle fibres require greater recovery periods?
2. Using Recovery Status Data to Individualise Recovery strategies Greatest Mechanical Loads: Accels/ decels, Dynamic actions Highest Locomotive Load: Max speeds attained, HI distance Physical Outputs (Relative to activity Level) Often greatest internal Load: mins> 85% MHR, HR Trimp High Explosive Players Heightened muscle damage from high-force eccentric actions Physical Responses Excessive depletion of phosphate stores Potential for greater neural fatigue:
2. Using Recovery Status Data to Individualise Recovery strategies Rational for this hypothesis - Fast twitch fibres demonstrate: Greater levels of neural fatigue during repeated 5 s MVCs (Hamada et al., 2003) Require higher neural activation thresholds = central drive issues!! Greater amounts of neurotransmitter secretion = central and peripheral issues!! Combined creates Enhanced Synaptic Depression in type II fibres HOW CAN NEURAL FUNCTION BE AFFECTIVELY ASSESSED?
Neural Function Assessment Traditional Direct Electrical Stimulation: Peripheral Can be delivered via surface or implanted electrodes
Neural Function Assessment Direct Electrical Stimulation: Central + Supra-spinal it s hard (and painful) to non-invasively stimulate the brain because the skull gets in the way Can also struggle to excite deep nerves
Alternative Technology: Transcranial Magnetic Stimulation TMS: What is it and how does it work? An alternative approach is to induce electrical fields in tissue via an electrical magnetic field (Magnetic Stimulation) An intense magnetic field pulse will induce electric fields approx. 300 V/m, and subsequent low level currents (Farady s Law of Induction) The induced current activates presynaptic elements that project to the output neurons, which then activate the muscle
Transcranial Magnetic Stimulation; A Solution?? Advantages of TMS Non-invasive + Relatively benign / painless Enables stimulation of deep neural structures Assess Central / Cortical + Peripheral neural function
Parameters Obtained from TMS Resting Motor Threshold Electrical stimulation required for a motor evoked response: Unit of TMS Dose (Goodall et al., 2012) Typically expressed as percentage of generator output Can provides information on Cortical excitability Fatigued state require greater magnetic impulse to create tetanus contraction
Parameters Obtained from TMS Motor Evoked Potential (MEP) MEP is an electrical potential recorded from a muscle following stimulation of the cortex via TMS MEP Latency = Central Motor Conduction Time MEP Amplitude = Corticospinal Excitability Information on the neural pathway from Cortex to Muscle Not specifically central fatigue
Parameters Obtained from TMS Cortical Voluntary Activation - Twitch Interpolation If MVC can be increased with TMS stimulation provides an index of central fatigue TMS Stimulation
Application of TMS Practical Considerations Measures require EMG analysis! Controlling variables: - Body Position - Agonist / Antagonist Strength Ratios - Identification of site of neural modulation? Adherence during maximal protocols
Application of TMS Evidence for the use of TMS in Sport and Exercise Neural adaptations to strength training (Carroll et al., 2009) Detected fatigue within and after a repeated sprint protocol (Goodhall et al., 2014) Exciting research as an indicator of over-reaching in cyclists (Ross et al., 2010)
Application of TMS Current and Future Directions Assessing the robustness and sensitivity of TMS parameters Creating a usable / practical framework to collect TMS data Begin collecting data on players within periods of intensive conditioning Correlate findings with different player types
In Summary The multi-faceted nature of football may require several measures of recovery status: fitting the needs of the player and the club However, effective measurement of neural fatigue is still not commonplace Yet such information is crucial to individualise recovery protocols TMS could provide a potential solution, early signs are promising
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