According to health surveys, between 20-50% of older adults in Europe and the USA report difficulties with activities of daily living (Heikkinen, 2008; Manton and Gu, 2001). One of the factors that contribute to this loss of functional capacity and mobility in older age is the progressive decline of skeletal muscle mass with increasing age (English and Paddon-Jones, 2010; Forbes and Reina, 1970). The presence of both low muscle mass and muscle strength is described by the syndrome of sarcopenia (Abellan van Kan et al., 2012; Cruz-Jentoft et al., 2010). The consequences of sarcopenia are often severe and can result in decreased postural control (Wolfson et al., 1995), increased incidence of falls (Moreland et al., 2004) and deficits in quality of life (Tsekoura et al., 2017) in older adults. Furthermore, the progressive loss of muscle mass during the aging process is accompanied by an increase in cardiometabolic risk factors leading to a higher incidence of type 2 diabetes or atherothrombotic diseases (Sayer et al., 2013). To maximize the period of effective functioning in older age, Cruz-Jentoft and Landi (2014) recommend comprehensive multidimensional approaches combining nutrition and physical exercise as main components of sarcopenia interventions. Concomitantly, common exercise guidelines aiming to increase muscle cross-sectional area (CSA) recommend using moderate to high training loads of 70-85% of individuals' one-repetition maximum (1RM) (ACSM, 2009). However, in a clinical setting and especially for older people with comorbidities, training with such heavy loads is often contraindicated or impossible (Gheno et al., 2012), due to comorbidities such as coronary heart diseases or joint and muscle impairments. Findings from previous studies have indicated that low-intensity resistance exercise in combination with blood flow restriction (BFR) promotes muscle mass increases similar to what is seen after high-load training with 80% 1RM (Vechin et al., 2015). Fry et al. (2010) have demonstrated that BFR training enhances protein synthesis by phosphorylating the mammalian target of rapamycin (mTOR) and its downstream effectors p70 ribosomal S6 kinase (S6K1) in older men. S6K1 has repeatedly been shown to regulate mRNA translation initiation and to be involved in training-induced hypertrophy (Baar and Esser, 1999). In parallel, evidence suggests that ingesting dietary protein additionally enhances the effects of prolonged resistance training on muscle mass and strength in younger and older people (Cermak et al., 2012). By activating the mTOR signaling pathway and thus protein synthesis, it is believed that branched chain amino acids (BCAAs) or di- and tripeptides such as hydroxyprolyl-glycine (Hyp-Gly) stimulate muscular hypertrophy (Cermak et al., 2012; Kitakaze et al., 2016). Previous studies showed that considerable amounts of Hyp-Gly have been found in human blood after the intake of collagen hydrolysate (CH) (Shigemura et al., 2011). Recent investigations in this field have also demonstrated that the daily ingestion of 15 g collagen peptides (CP) is an effective strategy for improving fat free mass and strength following high-load resistance training in older men (Zdzieblik et al., 2015).
Therefore, the purpose of this study was to examine the influence of BFR training with collagen hydrolysate supplementation on muscle mass and function in older men at risk of sarcopenia. We hypothesized that this training method is a promising alternative in order to counteract the age-related decline in muscle mass and is therefore beneficial for populations who are not capable of lifting near-maximum loads. Additionally, reactive oxygen species (ROS) and insulin-like growth factor-1 (IGF-1) were measured, since both play crucial roles in muscular remodeling and promote cellular adaptations (Powers et al., 2010). As a second aim, we wanted to determine whether a collagen hydrolysate supplementation enhances the effects of this training modality.
Thirty-nine healthy older men aged 50 years or older were recruited to participate in this study. All participants were apparently healthy with a regular physical activity level being less than 60 minutes per week assessed with the Freiburg Questionnaire of physical activity (Frey et al., 1999). Exclusion criteria included the presence of a chronic illness, history of deep vein thrombosis, uncontrolled hypertension, kidney failure, cardiovascular diseases and smoking. Additionally, participants with acutely elevated D-dimer concentrations (> 0.5 mg/l) or intolerance against collagen hydrolysate or silicon dioxide were not included. All participants were advised not to change their regular physical activity or eating behaviors during the intervention. Two participants did not meet the inclusion criteria due to regular smoking and elevated D-dimer concentrations and were thus excluded before assignment to any of the groups.
The study was approved by the local ethics committee of the University of Freiburg (356/17) and conducted in accordance with the Declaration of Helsinki. Experimental procedures and potential risks were explained before informed consent was obtained prior to participation. A total of 30 participants completed the investigation and none of the dropouts was due to side effects of training.
A prospective, randomized, placebo-controlled design was implemented. Before the 8-week intervention period, the participants were randomly allocated into one of the following three groups: BFR training with collagen supplementation (BFR-CH), BFR training with placebo (BFR-PLA) or a group that had no training but collagen supplementation only (CON). Allocation sequence was concealed in order to prevent selection bias (Schulz et al., 2010). Both training groups and all therapists and outcome assessors were blinded, whereas the CON group was not blinded.
One week prior to the start of the intervention, all participants were screened using a comprehensive anamnesis screen, physical examination, as well as blood draws for the measurement of safety parameters such as hemogram, creatinine, urea, aspartate transaminase, alanine aminotransferase and D-dimer. Furthermore, isometric leg strength, metabolic parameters, and thigh muscle cross-sectional measured by magnetic resonance imaging (MRI) were determined within one week before and after the intervention.
During the 8-week intervention, the BFR-CH and BFRPLA groups completed a lower extremity training program on three days of the week, with at least one day rest between consecutive sessions. For all these participants, a training session consisted of one set of 45[degrees] leg press exercise (FREI AG, Kirchzarten, Germany) with 30 repetitions at 20% of their individual 1RM, followed by three sets of 15 repetitions with 30s inter-set rest periods. This is a common low-intensity BFR exercise protocol reported in recent research (Vechin et al., 2015). Additional 1RM tests were implemented every two weeks (6 sessions) to progressively adjust training load to the current strength level of each individual. At mid-point of the intervention period (after week 4, 12 sessions) the training load was increased from 20% 1RM to 30% 1RM. A metronome was used during each session to ensure that the participants held a tempo of 2 seconds for concentric and 2 seconds for eccentric muscle action.
Arterial occlusion pressure (AOP) for each participant was recorded in a sitting position from both legs with a 12-cm-wide pneumatic nylon tourniquet (Zimmer Biomet, Warsaw, Indiana, USA) applied at the most proximal portion of each thigh. This cuff position corresponded to the training position for the cuff. AOP was calculated after the cuff pressure was successively increased until a pulse was no longer detected at the posterior tibial artery by Doppler ultrasound (Handydop, Kranzbuhler, Solingen, Germany). At this point, an arterial occlusion of 100% was assumed.
The same pneumatic nylon tourniquet was used for all BFR training sessions and kept inflated by a computerized tourniquet system (A.T.S. 3000, Zimmer Biomet, Warsaw, IN, USA) at 50% of each individual's AOP during the entire session including rest periods. To consider the participants' current blood pressure, this AOP determination method was conducted immediately before every training session. All the prescribed repetitions per set were successfully completed by all individuals.
All participants were instructed to maintain their dietary habits during the intervention period. Nutritional status was examined using Nutriguide 4.6 Software (Nutri Science GmbH, Hausach, Germany). Participants recorded their dietary habits during three consecutive days, including two weekdays and one day...