Collagen and Vitamin C Supplementation Increases Lower Limb Rate of Force Development Dana M. Lis, 1 Matthew Jordan, 2 Timothy Lipuma, 1 Tayler Smith, 1 Karine Schaal, 1 and Keith Baar 1,3 1 Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, USA; 2 Canadian Sport Institute Calgary, Calgary, AB, Canada; 3 Physiology and Membrane Biology, University of California Davis, Davis, CA, USA Background: Exercise and vitamin C-enriched collagen supplementation increase collagen synthesis, potentially increasing matrix density, stiffness, and force transfer. Purpose: To determine whether vitamin C-enriched collagen (hydrolyzed collagen [HC] + C) supplementation improves rate of force development (RFD) alongside a strength training program. Methods: Using a double-blinded parallel design, over 3 weeks, healthy male athletes (n = 50, 18–25 years) were randomly assigned to the intervention (HC + C; 20 g HC + 50 mg vitamin C) or placebo (20 g maltodextrin). Supplements were ingested daily 60 min prior to training. Athletes completed the same targeted maximal muscle power training program. Maximal isometric squats, countermovement jumps, and squat jumps were performed on a force plate at the same time each testing day (baseline, Tests 1, 2, and 3) to measure RFD and maximal force development. Mixed-model analysis of variance compared performance variables across the study timeline, whereas t tests were used to compare the change between baseline and Test 3. Results: Over 3 weeks, maximal RFD in the HC + C group returned to baseline, whereas the placebo group remained depressed (p = .18). While both groups showed a decrease in RFD through Test 2, only the treatment group recovered RFD to baseline by Test 3 (p = .036). In the HC + C group, change in countermovement jumps eccentric deceleration impulse (p = .008) and eccentric deceleration RFD (p = .04) was improved. A strong trend was observed for lower limb stiffness assessed in the countermovement jumps (p = .08). No difference was observed in maximal force or squat jump parameters. Conclusion: The HC + C supplemen- tation improved RFD in the squat and countermovement jump alongside training. Keywords: performance, glycine, training, tendon, speed Rate of force development (RFD) is highly correlated with sport performance that requires maximal mechanical power and speed (Lamas et al., 2012; Tillin et al., 2013) including weightlifting (Haff et al., 2005; Hornsby et al., 2017), jumps, throws (McLellan et al., 2011; Nuzzo et al., 2008), cycling (Stone et al., 2004), and sprinting (Slawinski et al., 2010). There are several determinants of RFD including muscle fiber type, neuromuscular activation, motor unit recruitment, and muscle-tendon unit stiffness (Buckthorpe & Roi, 2017). Various forms of training improve RFD in the general or untrained population. However, only high velocity and ballistic training have been shown to improve RFD in trained athletes (Lamas et al., 2012; Tillin et al., 2013). This type of training increases neural drive (motor unit recruitment and rate coding) and increases muscle-tendon unit stiffness (Earp et al., 2011). Recent work suggests that collagen-based tissues (i.e., ligament, tendon, cartilage) are more dynamic than previously appreciated with similar turnover rates to skeletal muscle tissue (0.02%–0.13% per hour; Earp et al., 2011; Kalliokoski et al., 2007; Laurent, 1987; Miller et al., 2005, 2007; Smeets et al., 2019). Connective tissue adaptations, including increased stiffness arising from greater colla- gen content and cross-linking, decrease the risk of injuries since tendon stiffness is linearly related to failure strength (LaCroix et al., 2013; Marturano et al., 2013). Acute exercise is known to increase collagen synthesis (Langberg et al., 1999, 2001; Miller et al., 2007) as well as the expression of the primary enzyme involved in collagen cross-linking, lysyl oxidase (Heinemeier et al., 2009). The result is a training-induced increase in connective tissue density and stiffness (Couppe et al., 2008; Kubo & Ikebukuro, 2019). While the relation- ship between exercise stimulus/loading and collagen synthesis is well established (LaCroix et al., 2013; Kubo & Ikebukuro, 2019), research on the role of dietary supplements that support these adaptations is in its infancy. Specifically, whether hydrolyzed collagen (HC) ingested prior to loading augments training-induced rates of collagen synthesis enough to measure changes in the capacity to rapidly generate muscle force (explosive strength) measured as the RFD is still theoretical. In order to have a measurable effect on the mechanical function of connective tissues, the ingested amino acids must be digested, absorbed, transported to the target tissue, and then integrated into de novo collagen protein. Several studies have demonstrated that gelatin or an HC supplement ingested prior to exercise increased delivery of key amino acids (e.g., high amounts of glycine, proline, hydroxyproline) to connective tissue which may augment collagen synthesis in vivo (Konig et al., 2018; Oesser et al., 1999; Shaw et al., 2017). Amino acid levels peak in the blood about 40–60 min after ingestion (Alcock et al., 2019; Walrand et al., 2008). Microdialysate samples from the Achilles tendon in both young (21–30 years of age) and old-aged (60–75 years of age) participants demonstrated that amino acid levels peaked in the peritendinous space after 135 min for the younger age group and ∼45 min for the older adults, following ingestion of a high proline, high glycine amino acid mix (Couture, 2020). In women with age- related reductions in bone mineral density, 12 months of supple- mentation with 5 g of collagen peptides improved bone mineral density and demonstrated a favorable shift in bone markers, indicating increased bone formation and reduced bone degradation Lis (dmlis@ucdavis.edu) is corresponding author, https://orcid.org/0000-0002- 9759-7901. 65 International Journal of Sport Nutrition and Exercise Metabolism, 2022, 32, 65-73 https://doi.org/10.1123/ijsnem.2020-0313 © 2022 Human Kinetics, Inc ORIGINAL RESEARCH Unauthenticated | Downloaded 07/01/22 03:59 AM UTC