Low-intensity tensile loading increases intratendinous glucose uptake in the Achilles tendon

Abstract

The metabolic activity of tendinous tissues has traditionally been considered to be of limited magnitude. However, recent studies have suggested that glucose uptake increases in the force-transmitting tissues as a response to contractile loading, which in turn indicates an elevated tissue metabolism. The purpose of the present study was to investigate whether such a mechanism could be observed for the human Achilles tendon following tensile loading. Six subjects participated in the study. Unilateral Achilles tendon loading was applied by 25-min intermittent voluntary plantar flexor contractions. A radioactive tracer ([18F]-2-fluoro-2-deoxy-D-glucose) was administered during muscle action, and glucose uptake was measured by use of PET. Regions of interest were defined on the PET images corresponding to the cross section of Achilles tendon at two longitudinally separated sites (insertion and free tendon). Glucose uptake index was determined within respective regions of interest for the active and resting leg. Tendon force during voluntary contractions was approximately 13% of maximal voluntary contraction force. Tendon loading induced an elevated glucose uptake index compared with that of the contralateral resting tendon in the region of tendon insertion (0.13 +/- 0.05 vs. 0.09 +/- 0.02; P < 0.05) and at the free tendon (0.12 +/- 0.01 vs. 0.08 +/- 0.02; P < 0.05). The present data suggest that tissue metabolism is elevated in the human Achilles tendon in response to low-intensity loading.

Prospective Evaluation of Physiologic Uptake Detected with True Whole-Body 18F-FDG PET/CT in Healthy Subjects

“…Bojsen-Moller et al (23) studied the effect of low-intensity tensile loading on the uptake of 18 F-FDG in the Achilles complex. In that study, subjects performed unilateral voluntary ankle plantar flexion at approximately 13% of the maximal voluntary contraction force.…”

Accuracy of MRI technique in measuring tendon cross‐sectional area

“…Tendons have traditionally been considered relatively inert structures, but several recent reports demonstrate that human tendons respond directly to physical activity by increased metabolism (Hannukainen et al, 2005;Kalliokoski et al, 2005;Bojsen-Moller et al, 2006) and increased collagen synthesis (Langberg et al, 1999(Langberg et al, , 2001Christensen et al, 2011). Furthermore, strength training and habitual loading of tendons appear to be associated with an increase in tendon size (Arampatzis et al, 2007;Kongsgaard et al, 2007;Couppe et al, 2008), confirming that the aforementioned responses to elevated loading result in a net increase in tendon tissue.…”

Uphill running improves rat Achilles tendon tissue mechanical properties and alters gene expression without inducing pathological changes

“…The rationale for trying to detect tendinopathy with use of 18 F-fluoro-deoxyglucose-PET is that cell density and vascularity is often increased in tendinopathic tendons (8,37), both of which would be expected to increase glucose uptake. In addition, it is possible to detect the increase in glucose uptake seen in response to acute exercise in rats and humans (9,29,43), and it seems likely that an increase in tendon metabolism, due to tendinopathy, would be within a similar range as the increase seen in response to exercise. We observed no difference between pre-and post-levels of glucose uptake at rest in the Achilles tendons of running rats, and also the glucose uptake was similar in controls and running rats at all time points (Fig.…”