The Handgrip Endurance Task as a Simple Clinical Indicator of Mental Fatigue in Patients with Chronic Low Back Pain.

Purpose: Mental fatigue is highly prevalent in chronic low back pain (cLBP) but rarely assessed in clinical practice. Standard physical capacity tests may underestimate functional abilities when mental fatigue is present. This study investigated whether a simple handgrip endurance task could objectively detect mental fatigue effects on physical performance in cLBP patients. Patients and Methods: One hundred twenty participants (60 cLBP patients, 60 pain-free controls) performed a handgrip endurance task at 13% of maximal voluntary contraction before and after either a mentally fatiguing Stroop task (30 minutes) or watching a neutral documentary. Time to exhaustion (TTE) was compared between conditions within each group using analysis of variance. Results: cLBP patients who performed the Stroop task showed significantly greater reduction in endurance (mean decrease: 118 seconds) compared to those who watched the documentary (mean decrease: 71 seconds), p <0.05. This mental fatigue effect was not observed in pain-free participants (p =0.644). Importantly, both groups performed similarly on the Stroop task itself, indicating that cognitive performance did not differ between populations. Conclusion: Mental fatigue selectively impairs physical endurance in cLBP patients. The handgrip endurance test offers a practical, low-cost tool to objectively assess mental fatigue in clinical settings. These findings have important implications for functional capacity evaluations and return-to-work assessments, as standard tests may systematically underestimate patients' true abilities when mental fatigue goes unrecognized.