Baxter Laboratory

Todd Hullfish


Doctoral Student, Biomedical Engineering, University of Pennsylvania, Philadelphia, PA, USA

Bachelors of Science, Mechanical Engineering, Drexel University, Philadelphia, PA, USA

Research Interests

I study how mechanical loading impacts functional outcomes in patients with Achilles tendon injuries. I have developed wearable sensor paradigms to accurately quantify tendon loading in the real-world - a critical next step towards identifying therapuetic loading profiles for these patients. I also have interests in ultrasound imaging to characterize tendon status and lab instrumentation that streamline clinical research studies to maximize patient recruitment and retention.


Drazan JF, Phillips WT, Seethapathi N, Hullfish TJ, Baxter JR. Moving outside the lab: Markerless motion capture accurately quantifies sagittal plane kinematics during the vertical jump. J Biomech 2021;125:110547.

Hullfish TJ, Drazan JF, Baxter JR. Experimental recommendations for estimating lower extremity loading based on joint and activity. J Biomech 2021;127:110688.

Schmidt EC, Hullfish TJ, O’Connor KM, Hast MW, Baxter JR. Ultrasound echogenicity is associated with fatigue-induced failure in a cadaveric Achilles tendon model. J Biomech 2020;105:109784.

Drazan JF, Hullfish TJ, Baxter JR. Novel isodamping dynamometer accurately measures plantar flexor function. J Biomech 2020;111:110015.

Baxter JR, Corrigan P, Hullfish TJ, O’Rourke P, Silbernagel KG. Exercise Progression to Incrementally Load the Achilles Tendon. Med Sci Sports Exerc 2021;53:124–30.

Drazan JF, Hullfish TJ, Baxter JR. Muscle structure governs joint function: linking natural variation in medial gastrocnemius structure with isokinetic plantar flexor function. Biol Open 2019;8:bio048520.

Hullfish TJ, O’Connor KM, Baxter JR. Medial gastrocnemius muscle remodeling correlates with reduced plantarflexor kinetics 14 weeks following Achilles tendon rupture. J Appl Physiol 2019;127:1005–11.

Hullfish TJ, O’Connor KM, Baxter JR. Gastrocnemius fascicles are shorter and more pennate throughout the first month following acute Achilles tendon rupture. PeerJ 2019;7:e6788.

Qu F, Stoeckl BD, Gebhard PM, Hullfish TJ, Baxter JR, Mauck RL. A Wearable Magnet-Based System to Assess Activity and Joint Flexion in Humans and Large Animals. Ann Biomed Eng 2018;46:2069–78.

Hullfish TJ, Qu F, Stoeckl BD, Gebhard PM, Mauck RL, Baxter JR. Measuring clinically relevant knee motion with a self-calibrated wearable sensor. J Biomech 2019;89:105–9.

Slater AA, Hullfish TJ, Baxter JR. The impact of thigh and shank marker quantity on lower extremity kinematics using a constrained model. BMC Musculoskelet Disord 2018;19:399.

Hullfish TJ, Baxter JR. A Reliable Method for Quantification of Tendon Structure Using B-Mode Ultrasound. J Ultrasound Med 2018;37:2419–24.

Baxter JR, Hullfish TJ, Chao W. Functional deficits may be explained by plantarflexor remodeling following Achilles tendon rupture repair: Preliminary findings. J Biomech 2018;79:238–42.

Hullfish TJ, Hagan KL, Casey E, Baxter JR. Achilles tendon structure differs between competitive distance runners and nonrunners despite no clinical signs or symptoms of midsubstance tendinopathy. J Appl Physiol 2018;125:453–8.

Drazan JF, Hullfish TJ, Baxter JR. An automatic fascicle tracking algorithm quantifying gastrocnemius architecture during maximal effort contractions. PeerJ 2019;7:e7120.

Hullfish TJ, Baxter JR. A simple instrumented insole algorithm to estimate plantar flexion moments. Gait Posture 2020;79:92–5.

Hagan KL, Hullfish TJ, Casey E, Baxter JR. Tendon Structure Quantified using Ultrasound Imaging Differs Based on Location and Training Type. J Appl Physiol 2018;125:1743–8.

Hullfish TJ, O’Connor KM, Baxter JR. Instrumented immobilizing boot paradigm quantifies reduced Achilles tendon loading during gait. J Biomech 2020;109:109925.

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