Returning to sport after an injury can be a long and cumbersome process. After all the hard work, time, and effort put forth during rehab, an athlete wants nothing more than for their return to the field to be a smooth and injury free process. Unfortunately, this is not the always the case. Re-injury rates when returning to sport are still much too high. It seems that as levels of cognitive demand increase, athletes struggle to transfer the gains made in rehabilitation to the field.(1)
For this reason, research over the last decade has really focused on the multifactorial nature of returning to sport and how clinicians can maximize their patient interventions to decrease re-injury risk. One notable research finding has been the impact of neurocognitive demand on performance quality and sEMG.
Neurocognitive function incorporates the visual attention, self-monitoring, agility/fine motor skills, processing speed, reaction time, and dual task requirements of a sport.(2) It can be measured by performance of these tasks as well as through neurocognitive computer tests (like the Stroop Test). (3,4) There are a finite number of cortical resources in the brain, there is a trade off in performance when motor and/or cognitive tasks are competing for the same resources.(1) Since cognitive tasks require most of the brain’s attention resources, working memory becomes overloaded and there is a reduction in both cognitive and motor performance.(5)
As cognitive load is increased after an injury, there is a subsequent impairment in motor performance.(1) This indicates that when an athlete has poor neurocognitive function, they may sacrifice their quality of movement when performing sudden changes in direction, landings, or unexpected motions.(2) For example, during an unanticipated side-step cutting motion, sEMG data demonstrated an increase in quad activation at initial contact and a decrease in the quad/hamstring co-contraction ratio for the group that scored lower on a neurocognitive test.(2) Additionally, ACL groups with lower neurocognitive function scores demonstrated an increase in peak vertical GRF, anterior tibial shear force, adduction moment, knee abduction angle, and decreased trunk flexion when landing.(2)
Let’s take a further look at how neurocognitive demands and fatigue effect movement patterns and EMG findings.
Dual Tasking and EMG
When asked to perform a drop vertical jump while simultaneously adding or subtracting, patients demonstrated a larger peak vertical GRF, decreased knee / hip flexion angles, and increased knee abduction moment at initial contact.(6) This means that a cognitive task led to a much stiffer landing position which adversely changes the biomechanics required for a safe/soft landing.(6) Furthermore, only 33-50% of people answered the mathematical problem correctly.(6)
Check out these video examples showing the impact a dual task has on the EMG during landing using mTrigger biofeedback.
Drop Vertical Jump
DVJ with Addition
DVJ with Subtraction
Neurocognitive Fatigue, Mental Performacne, and EMG
In some studies, cognitive fatigue from prolonged mentally demanding tasks can lead to a change in muscle strength and activity.(7) The increase in cognitive demand, impacts levels of neuromuscular fatigue and reduces the ability of a muscle to produce a desired force.(7) In one study, looking at the effects of repeated hand gripping after cognitive fatigue found that when under cognitive fatigue, there was a decrease in EMG activity of the flexor carpi radialis and extensor carpi radialis and an 18.7% decrease in endurance time.(7)
*Note: Strength loss is considered the gold standard for measuring muscle fatigue(7) however, there is not a direct correlation between EMG and strength. Yet, this demonstrates how EMG information can show the effects of fatigue and neurocognitive demand on performance.
Neurocognitive Demand and Motor Performance
When cognitive load is increased through dual tasking, deficits are seen in balance, gait, and performance in individuals with ACL injury, ankle sprain, and low back pain.(1) These deficits appear to increase proportionately with the difficulty of the task and subsequent cognitive load.(1) For instance, when under dual task conditions gait speed and cadence decrease.(1)
In another example, when a cognitive task is added to a motor task, it negatively impaired the knee force production sense in young male soccer players.(5) When asked to produce 50% maximal force (as measured by EMG) under dual task situations, players tended to grossly overestimate the amount of force they were producing.(5) When the cognitive demand was increased, the discrepancy in force production was even greater.(5)
Research is heavily pointing to the need for training increased cognitive demand, dual tasking, and challenging decision making in the clinic.(1) sEMG information can be used in this situation to measure, analyze, and track progress. By doing so, we can aim to better prepare individuals for the challenges and neurocognitive demands of the sporting environment.(8)
Motor Learning with Biofeedback
mTrigger Biofeedback for ACL Injuries
1. Burcal CJ, Needle AR, Custer L, Rosen AB. The Effects of Cognitive Loading on Motor Behavior in Injured Individuals: A Systematic Review. Sports Medicine. 2019;49(8):1233-1253. doi:10.1007/S40279-019-01116-7/METRICS
2. SHIBATA S, TAKEMURA M, MIYAKAWA S. The influence of differences in neurocognitive function on lower limb kinematics, kinetics, and muscle activity during an unanticipated cutting motion. Phys Ther Res. 2018;21(2):44. doi:10.1298/PTR.E9938
3. Porter K, Quintana C, Hoch M. The Relationship Between Neurocognitive Function and Biomechanics: A Critically Appraised Topic. J Sport Rehabil. 2020;30(2):327-332. doi:10.1123/JSR.2020-0103
4. Scarpina F, Tagini S. The stroop color and word test. Front Psychol. 2017;8(APR):241674. doi:10.3389/FPSYG.2017.00557/BIBTEX
5. Özalp M, Demirdel E. Does secondary cognitive task affect knee force production sense in young male soccer players? Spor Hekimliği Dergisi. 2022;57(3):142-146. doi:10.47447/TJSM.0641
6. Imai S, Harato K, Morishige Y, et al. Effects of Dual Task Interference on Biomechanics of The Entire Lower Extremity During the Drop Vertical Jump. J Hum Kinet. 2022;81(1):5. doi:10.2478/HUKIN-2022-0001
7. Shortz AE, Pickens A, Zheng Q, Mehta RK. The effect of cognitive fatigue on prefrontal cortex correlates of neuromuscular fatigue in older women. J Neuroeng Rehabil. 2015;12(1):1-10. doi:10.1186/S12984-015-0108-3/TABLES/2
8. Chaput M, Ness BM, Lucas K, Zimney KJ. A Multi-Systems Approach to Human Movement after ACL Reconstruction: The Nervous System. Int J Sports Phys Ther. 2022;17(1):47-59. doi:10.26603/001C.30020