Running is a lifelong activity (Koplan et al., 1995) that has considerable health benefits for people of all ages (Junior et al., 2015). One of the biggest reasons for running dropout is injury (Fokkema et al., 2019). Each runner experiences a 46% - 92% chance of injury every year (Benca et al., 2013). Approximately two thirds of runners are forced to interrupt their normal training schedule due to an injury (Benca et al., 2013).
One common overuse pathology that afflicts runners is Achilles tendinopathy (Paavola et al., 2002; Heckman et al., 2009; Kvist, 1994) which affect up to 52% of elite distance runners (Kujala et al., 2005). Runner's Achilles tendon injuries are thought to be the result of repetitive loading of the tendon, which results in disruption of tendon fibers, causing dysfunction and pain (Paavola et al., 2002). One predisposing risk factor for Achilles tendinopathy is limited dorsiflexion range of motion (Kvist, 1994; Lorimer and Hume, 2014). Limited dorsiflexion is thought to increase subtalar ankle pronation (Kvist, 1994), resulting in excessive force and tension leading to Achilles tendinopathy (Clement et al., 1984, Becker et al., 2017).
In an attempt to prevent Achilles tendon injury many runners perform stretching before and/or after exercise (Welsh and Clodman, 1980). Stretching reduces muscle and tendon stiffness (Kay et al., 2015; Konrad et al., 2017), is thought to increase muscle length, and prepares the muscle and tendon for activity (Park and Chou, 2006; Shehab et al., 2006). While stretching is reported to have no effect on all cause injury, it might have some mediating effect on acute muscle injuries associated with running, sprinting, or other repetitive contractions (Behm et al., 2015). Thus, most coaches, athletes, and clinicians still favor including stretching within a training program (Shehab et al., 2006). Stretching has been shown to increase dorsi-flexion range of motion effectively in as little as three weeks (Dinh et al., 2011; Peres et al., 2002; Johanson et al., 2009).
Tendons adapt to the stresses imposed upon them (Kubo et al., 2002; Reeves et al., 2003; Tardioli et al., 2012), leading to changes in tendon cross sectional area (CSA), length, thickness, and stiffness (Wilson and Lichtwark, 2011; Tardioli et al., 2012). These adaptations are seen acutely and in long term situations. Acutely, tendon CSA decreases following a single bout of running (Tardioli et al., 2012; Neves et al., 2014). In long term situations, tendon CSA has been shown to increase in response to running in 3 weeks (Sponbeck et al., 2017). It is not understood if long-term intervention training impacts acute responses of tendons to exercise.
Ultrasound imaging is a reliable (Neves et al., 2014) and non-invasive method used to assess tendon structure and CSA changes (Farris et al., 2011; Martinoli et al., 2002). Ultrasound use is increasing to assess function and injury in many sports medicine settings. It allows for detailed assessment of tendons and dynamic testing of tendon integrity (Jacobsen, 2018).
To date, no studies exist to our knowledge that examine how a stretching regimen alters the tendon response to a bout of running. Since limited dorsiflexion is a risk factor for Achilles tendinopathy (Kvist, 1994), increasing dorsiflexion may decrease Achilles tendinopathy risk. Therefore, the aim of this study was to examine if a three-week stretching program alters Achilles CSA response to a 20-minute run. We hypothesized that the magnitude of within session changes in Achilles tendon CSA will be greater in response to a three-week triceps surae stretching program.
This was a randomized controlled interventional study.
Thirty-three runners (16 female, age = 23.31 [+ or -] 4.31 years, height = 1.65 [+ or -] 0.10 m, mass = 57.12 [+ or -] 8.12 kg, running history = 8.88 [+ or -] 4.13 years, weekly mileage = 29.23 [+ or -] 50.77 miles and 17 male, age = 26.71 [+ or -] 4.71 years, height = 1.83 [+ or -] 0.10 m, mass = 75.12 [+ or -] 16.12 kg, running history = 10.35 [+ or -] 7.35 years, weekly mileage = 20.88 [+ or -] 39.12 miles) completed this study (Table 1). Participants were recruited from local universities and running centers via fliers and announcements. Their running experience ranged from recreational to sub-elite athletes. None of the participants consistently stretched the Achilles tendon for one month prior to participation in the study. They had not suffered an Achilles tendon injury within six months, a lower extremity injury within three months of data collection, or were pregnant. Participants were currently running at least 3 times per week and able to run 5000m in under 24:00 min. All procedures were granted approval by the Institutional Review Board at the university (study protocol x15033). Power assessment indicated that with a mean of .36 [cm.sup.2] and SD of 0.04 [cm.sup.2], sixteen participants were needed to detect a significant difference of .4 [cm.sup.2] between pre and post-run Achilles tendon CSA measurements at (p = 0.05, B = 0.8). Thirty five participants started the study (18 control group, 17 treatment group). One participant dropped out of treatment group because the stretching was causing pain to the Achilles tendon and another dropped out from the control group due to an unrelated injury that prevented further participation.
Participants read and signed an informed consent and completed a pre-participation questionnaire to determine eligibility before starting data collection. They were then scheduled for their running visits, a pre-intervention run and a post-intervention run, separated by three weeks per previously published protocols. (Magnusson et al., 1996; Toft et al., 1989)...