One of the most widely spread sport injuries among athletes is ankle sprains. It is assumed that 31-40% of athletes with an ankle sprain suffer from permanent impairments. The progression of recurrent ankle sprains and residual symptoms is designated as chronic ankle instability (CAI). Athletes with CAI complain about chronic symptoms of giving way, pain, weakness and general instability, which can affect the activities of daily living, functional activities and physical exercise (Hubbard, 2008; Hubbard and Hertel, 2006).
Therapeutic approaches for CAI should primarily address the prophylaxis and occurrence of injuries. In addition to medical treatment, physiotherapy and sports therapeutic interventions focusing on the improvement of neuromuscular, proprioceptive and strength deficits (Holmes and Delahunt, 2009), nutritional supplementation should also be considered. The affected target tissue of the ankle joint is comprised of approximately 70% collagen. It is responsible for the elasticity and firmness of tendons, ligaments and connective tissues and therefore constitutes one of the most predominant components of the extracellular matrix (Kjaer et al., 2009).
Specific collagen peptides are produced for nutritional administration by a special hydrolysis of collagen. On the basis of their organoleptic and hydrological characteristics, collagen peptides can easily be digested in drinks or dietary supplements (Mohammad et al., 2014; Shoulders and Raines, 2009). In general, the high biological availability of the peptides is based on its low molecular weight and its lack of cross links. Preclinical (Oesser and Seifert, 2003; Walrand et al., 2008) and human studies (Iwai et al., 2005; McAlindon et al., 2011) indicate that collagen peptides are almost completely resorbed after oral intake and that a considerable proportion accumulates in tissue structures (Oesser et al., 1999). Approximately 10% of CP is directly transferred in intact form with a size of 1-10 kDa from the gastrointestinal tract into the blood and may stimulate extracellular matrix expression and biosynthesis within the connective tissue (Ohara et al., 2007; Watanabe-Kamiyama et al., 2010).
Regarding the health of ligaments and tendons, it has been demonstrated that SCP improve the functional and mechanical properties of the connective tissue. An in vitro experiment revealed a significantly increased RNA expression and biosynthesis of collagen type I, collagen type III, proteoglycans and elastin in both ligament fibroblasts and the Achilles tendon, which were isolated by enzymatic digestion and seeded in monolayer cultures in a humidified incubator (Schunck and Oesser, 2013). Moreover, an in vivo study demonstrated that collagen hydrolysate intake increased circulating blood levels of glycine, proline, hydroxyproline and hydroxylysine (Shaw et al., 2017). In this investigation, the functional effects of collagen supplementation were examined by means of a mechanical approach. The study demonstrated that the tensile load of the investigated ligaments, the material properties in terms of stiffness, and the ultimate tensile strength increased following collagen peptide supplementation.
With respect to joint-related discomforts, a randomized, double-blinded and placebo-controlled investigation showed a reduction in activity-related joint pain in athletes with functional knee discomfort following the oral administration of 5 g SCP over 12 weeks (Zdzieblik et al., 2017). An additional study demonstrated that the supplementation of 10 g collagen peptides per day over a period of 6 months improved the firmness of tissue and its resistance to mechanical stress. This effect was particularly observable in persons with a high joint laxity at the beginning of the study (Weh and Petau, 2001). However, evidence regarding the impact of collagen peptides on CAI is limited. To the best of our knowledge, there are currently no studies evaluating the influence of SCP supplementation on subjects with CAI.
Considering the clinical relevance of these results, the effects of SCP could also have a therapeutic benefit on subjects with CAI. The purpose of the present study was to investigate the impact of SCP vs. placebo ingestion in subjects with chronic ankle instability by measuring the subjective function and mechanical stability of the ankle. The hypothesis being that SCP may improve ankle stability.
Sixty male and female athletes aged 26.9 (SD 9.1); weight 69.4 (SD 11.5) kg; height 1.74 (SD 0.09) m; with a CAIT score of 18.14 (SD 5.4) were recruited via existing databases and an article in a local newspaper (Figure 1). In this study competitive athletes were included (e.g. soccer, track and field athletes, basketball). All athletes were on an amateur competition level with 2-3 training sessions per week, but were not in an active competitive season. The subjects engaged inside and outside training sessions, respectively. In conformity with the International Ankle Consortium (IAC), only participants with CAI were included in the investigation. In this context, a medical examination was conducted by the principal investigator to verify, whether the participants have a history of at least 1 significant ankle sprain (Gribble et al., 2014). Second, we used the Cumberland Ankle Instability Tool (CAIT), a specifically, self-reported ankle instability specific evidence-based questionnaire. The primary inclusion criterion was a CAIT score of
The study was a randomized, double-blind and placebo-controlled design in which the participants supplemented either 5 g SCP (Gelita AG, Germany) or 5 g Maltodextrin (MDX). Both water-soluble preparations were comparable in terms of taste and appearance for daily oral ingestion over a period of 6 months. It is assumed that the acute and chronic loading of connective tissue is necessary to ensure the increased synthesis and turnover of extracellular matrix proteins, especially for collagen formation and degradation (Kjaer et al., 2009). Therefore, a mechanical loading protocol was applied in both groups that consisted of 3 home-based exercise sessions per week, which were performed within 10 minutes. They were scheduled with a day of rest between each session (e.g. Monday, Wednesday and Friday) and performed in the following order: rope skipping, squats, and one-legged heel raises. Rope skipping took 5 minutes. The squats and one-legged heel raises were performed in 1 set with 15 repetitions. The intensity was not increased throughout the entire intervention period. The participants consumed the supplements within 1 hour after completing each mechanical loading session.
On days without mechanical loading protocol, subjects...