Introduction: We studied the ability of clinicians to identify quadriceps motor points using a transcutaneous electrical stimulation unit (TENS). Methods: Twenty-two certified athletic trainers and 1 expert-rater identified the 7 motor points of the quadriceps at 2 time-points separated by 1 week. The difference was calculated between where each participant and the expert-rater identified each motor point using an x-y coordinate system. Bland-Altman plots were used to compare differences between 2 testing sessions. Results: No differences were observed between participants and the expert-rater for motor point location. The smallest variability in the limits of agreements were observed in the distal vastus medialis oblique (-1.89 to 1.86 cm) and proximal vastus lateralis (-1.61 to 2.35 cm). Discussion: Our results suggest the utilization of a TENS unit may be 1 way to identify quadriceps motor points to improve electrical stimulation applications. The smallest limits of agreement were over the most common quadriceps electrical stimulation electrode positions. Muscle Nerve 57: E1-E7, 2018Neuromuscular electrical stimulation (NMES) is a commonly used modality to aid in the restoration of muscle function and prevention of atrophy after injury or a surgical procedure. [1][2][3] The quadriceps muscles are a common treatment site for NMES, used for patellofemoral pain, 4 knee osteoarthritis, 5 and anterior cruciate ligament reconstruction. 2,6 However, despite frequent clinical use of NMES, evidence for its efficacy is mixed due to methodological inconsistencies and functional limitations. 7,8 The most common limitations of NMES include pain and muscle fatigue or damage. 8 It has been shown that, to strengthen a muscle, the stimulus intensity must be >60% of an individual's maximum volitional contraction. 9-11 A higher amplitude will result in more muscle fibers being recruited, and a linear relationship exists between amplitude and force production. 12 However, increasing the amplitude results in excitation of free nerve endings and nociceptive receptors, resulting in patient discomfort and limiting the ability of participants to reach the 60% volitional threshold. [13][14][15][16] Muscle fatigue is an additional concern due to altered muscle fiber recruitment patterns when electrically stimulated. Endogenous contractions recruit smaller, slow-twitch fibers first followed by larger, fast-twitch fibers. 17,18 This differs from electrically induced contraction, which is spatially fixed and depolarizes the same large-diameter, fast-fatiguing neurons more frequently. 17 Repeated electrically stimulated contraction leads to a decline in force production and increases potential muscle damage. 18,19 Therefore, utilizing an NMES treatment that can increase force production while minimizing the amplitude required, minimizing pain and fatigue, may optimize its clinical application.Researchers have identified that NMES applied directly over the muscle's motor points can increase maximum tolerated intensity, and can dec...
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