Capacity Versus Performance of Volitional Head Turns After Mild Traumatic Brain Injury

OBJECTIVE: To compare head motion capacity during a prescribed in-laboratory task with head motion performance in free-living daily life in individuals with mild traumatic brain injury (mTBI) and healthy controls. A secondary objective was to assess whether in-laboratory peak head motion metrics were associated with near maximal (95th percentile) free-living movements. SETTING: Research laboratory and participants' daily environments over 7 days of continuous monitoring. PARTICIPANTS: Twenty-three adults participated: 10 individuals with subacute, symptomatic mTBI (5F; age 30.3 (7.7) years; 35.2 (20.1) days postinjury) and 13 healthy controls (7F; age 31.9 (9.6) years). Participants were free of neurological, musculoskeletal, or balance-affecting conditions. DESIGN: Observational study combining a laboratory gait task with horizontal head turns and a 7-day free-living monitoring period using wearable inertial sensors on the head and lumbar spine. MAIN OUTCOME MEASURES: In-laboratory head turn amplitude and peak angular velocity (capacity); daily-life amplitude and angular velocity distributions (mean, median, 95th percentile), intra- and interday variability (performance); and associations with free-living measures. RESULTS: Individuals with mTBI demonstrated slower in-laboratory head turns than controls (223.53 (62.32) deg/s versus 302.01 (55.88) deg/s; P = 0.006), with no difference in amplitude. Daily-life amplitude and velocity did not differ between the groups. However, mTBI participants showed consistently smaller intra- and interday variability (P < 0.05), indicating more constrained daily movement patterns. Associations between in-laboratory peaks and free-living 95th percentile values were weak (r = -0.22 for amplitude; r = 0.10 for angular velocity). CONCLUSION: Although mTBI participants show reduced head motion capacity in laboratory tasks, their average daily-life kinematics are comparable to healthy adults. Reduced variability suggests constrained free-living movement strategies. These findings highlight the dissociation between capacity and performance and support integrating both laboratory assessments and continuous monitoring as complementary measures to fully characterize motor behavior following mTBI.