Forward Head Posture and Trunk Muscle Activation Patterns During a Rapid Leg-Raise Task in Asymptomatic Young Adults: A Cross-Sectional Study

Background/Objectives: Forward head posture (FHP) has been associated with alterations in cervical sensorimotor function; however, its relationship with trunk muscle activation during dynamic movement tasks remains incompletely understood. This study examined whether individuals with FHP demonstrate differences in the timing and magnitude of trunk muscle activation during a rapid lower-limb movement task. Methods: One hundred asymptomatic young adults (18–25 years) were classified as having normal head posture (NHP; craniovertebral angle (CVA) > 55°) or forward head posture (FHP; CVA < 50°) using PostureScreen® Mobile. Surface electromyography (EMG) was recorded bilaterally from the external oblique (EO), lumbar multifidus (MF), and the transversus abdominis/internal oblique region (TrA/IO) during ten externally cued right-leg raises. EMG amplitude and onset latency relative to rectus femoris activation were extracted for each muscle. Two multivariate analyses of variance (MANOVA) assessed overall group differences in EMG amplitudes and onset latencies. Significant multivariate effects were followed by univariate ANOVAs. Group × Side mixed-model ANOVAs evaluated side-to-side activation patterns. Pearson correlation and regression analyses examined correlations between craniovertebral angle (CVA) and EMG variables. Results: MANOVA revealed significant overall differences between the FHP and NHP groups for EMG amplitude (Wilks’ λ = 0.20, F(6,93) = 62.14, p < 0.001, η2p = 0.80) and onset latency (Wilks’ λ = 0.10, F(6,93) = 133.73, p < 0.001, η2p = 0.90). Follow-up ANOVAs showed significant differences for all EMG variables (all p < 0.001), with large effect sizes (Cohen’s d = 1.0–3.2). Mixed-model ANOVAs demonstrated significant Group × Side interactions (all p < 0.05). CVA showed significant moderate to strong correlations with EMG amplitude and onset latency measures (r = 0.43–0.79). Conclusions: FHP was associated with later trunk muscle activation and altered EMG activation patterns during the leg-raise task, including reduced activity recorded from the TrA/IO region and increased EO activation. These findings suggest FHP is associated with different trunk neuromuscular activation strategies during dynamic tasks. Despite consistent CVA–EMG associations, extreme multicollinearity limits the interpretation of CVA as an independent predictor.