Short reportThe influence of ultrasound measurement techniques on the age-related differences in Achilles tendon size
Introduction
The Achilles tendon (AT) is a large viscoelastic tissue that transmits force from the plantarflexor musculature to the calcaneus resulting in joint and limb movement. It undergoes large loads during activities of daily living (Magnusson et al., 2008) and has shown to be a metabolically active tissue that responds to chronic loading and unloading (Magnusson et al., 2008). Furthermore, the AT is susceptible to a high rate of injury which may be due to its “low safety factor” during high-intensity activities (Magnusson et al., 2003).
Aging is accompanied by changes in maximal and rapid strength (i.e. rate of force development) (Thompson et al., 2014) resulting in impaired locomotor function which may subsequently lead to a higher risk of falls and poorer quality of life (Beaudart et al., 2015). Previous studies have indicated that the age-related changes in tendinous tissues have a significant influence on muscular function (Stenroth et al., 2012) and injury risk (Magnusson et al., 2003). Animal models have demonstrated aging results in tendon hypertrophy (Tsuchida et al., 1997, Kotani et al., 1998), however these findings are inconsistent in humans (Magnusson et al., 2003, Pang and Ying, 2006, Carroll et al., 2008). It is possible that these discrepancies may be due to the measurement technique of AT size. For instance, Pang and Ying (2006) recently demonstrated that older participants (> 50 years) had greater AT cross-sectional area (CSA) when compared to younger participants using ultrasonography (US), however there were no age-related differences reported in AT thickness. Previous authors (Ekizos et al., 2013) have also questioned the reliability of US imaging to examine tendon morphology, which may indicate that future studies are needed to determine the most appropriate and reliable measure for investigating AT size. Thus, the purpose of the present study was to 1) examine the age-related differences in AT size using CSA and thickness in young and older adults and 2) determine the test–retest reliability and minimal difference values to determine a difference or change in AT size that can be considered real (Weir, 2005).
Section snippets
Participants
Nineteen young (mean ± SD: age = 19.8 ± 2.3 years; body mass = 69.2 ± 9.3 kg; height = 169.6 ± 14.6 cm) and 18 older (age = 69.4 ± 3.1 years; body mass = 81.6 ± 11.6 kg; height = 176.1 ± 3.7 cm) healthy, recreationally active (1–5 h a week of exercise) men volunteered for this study. All participants were free from any current or ongoing neuromuscular disease or musculoskeletal injuries of the foot, knee, or hip. This study was approved by the institutional review board for the protection of human subjects.
Research design
Each participant
Results
The older men had greater body mass (P = 0.001), but were similar in stature (P = 0.08) to the younger men. The older men (64.49 ± 13.87 mm2; 95% confidence intervals (CI) = 58.08–70.90 mm2) had greater AT CSA (P < 0.001) than the younger men (44.12 ± 16.04 mm2; 95% CI = 33.63–54.61 mm2). When accounting for body mass as a covariate, AT CSA remained significantly larger in the older men (P = 0.01). However, there was no difference in AT thickness (P = 0.96) between the younger (4.94 ± 0.46 mm; 95% CI = 4.73–5.15 mm) and
Age-related differences
The primary findings of this cross-sectional study indicated that older men exhibited larger AT CSA than younger men prior to and after accounting for differences in body mass; however, there was no difference in AT thickness between age groups. The results from previous studies using magnetic resonance imaging (MRI) and US are in agreement with our findings and indicated that AT CSA was greater in older adults. For example, Stenroth et al. (2012) and Magnusson et al. (2003) found AT CSA to be
Conclusion
In summary, the findings of the present study demonstrate an age-related increase in AT size that was only detected with the CSA assessments. Although both CSA and thickness measurements demonstrated acceptable reliability (Table 1), future studies examining changes among different populations, conditions, or following exercise interventions may wish to use CSA measurements as these may be more sensitive to detect changes in AT size.
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