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Neil Chapman, John Whitting, Suzanne Broadbent, Zachary Crowley-McHattan and Rudi Meir

A systematic literature search was conducted to review the evidence of residual force enhancement (RFE) in vivo human muscle. The search, adhered to the PRISMA statement, of CINAHL, EBSCO, Embase, MEDLINE, and Scopus (inception—July 2017) was conducted. Full-text English articles that assessed at least 1 measure of RFE in vivo voluntarily contracted human skeletal muscle were selected. The methodologies of included articles were assessed against the Downs and Black checklist. Twenty-four studies were included (N = 424). Pooled Downs and Black scores ranked “fair” (x¯=17 [2.26]). RFE was observed in all muscles tested. Joint range of motion varied from 15° to 60°. Contraction intensities ranged from 10% to >95% maximum. Although transient force enhancement during the stretch phase may change with angular velocity, RFE in the subsequent isometric phase is independent of velocity. The magnitude of RFE was influenced by smaller stretch amplitudes and greatest at joint angles indicative of longer muscle lengths. Contraction and activation intensity influenced RFE, particularly during the initial isometric contraction phase of a poststretch isometric contraction. RFE resulted in increased torque production, reduced muscular activation, and enhanced torque production when the neuromuscular system is weakened seen in an aged population.

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Michael F. Joseph, Jeffrey M. Anderson, Thomas H. Trojian and John Crowley


Achilles tendon rupture is often the result of a long-term degenerative process, frequently occurring asymptomatically.


To determine the prevalence of asymptomatic Achilles tendinopathy in an active, asymptomatic, young-adult population and to compare these findings across gender.


Convenience sample, cohort study.


Research laboratory


A sample of 52 (28 male, 24 female) healthy, active subjects were recruited from the student body at the University of Connecticut. Images of 104 Achilles tendons were made.


Ultrasound images made with a Phillips HD11 with a 15-MHz real-time linear-array transducer were collected on both the longitudinal and transverse axes of the Achilles tendon. Activity level was measured with the International Physical Activity Questionnaire Short Form (IPAQ-SF).

Main Outcome Measure:

Presence of ultrasound evidence of Achilles tendinopathy as agreed on by 2 blinded assessors highly skilled in ultrasonography.


More subjects were categorized as highly active (57.4%) on the IPAQ-SF than moderately active (42.6%). One female and one male subject were found to have ultrasound evidence of asymptomatic Achilles tendinopathy, equaling 3.8% prevalence in this study.


We found a low prevalence of asymptomatic Achilles tendinopathy in an active, young-adult population. Further work is necessary to identify an optimal group warranting ultrasound screening for asymptomatic tendinopathy.