Introduction Tendinopathy is a significant problem in elite athletes. Collagen supplementation has been shown to increase collagen synthesis, but it remains unknown whether collagen supplementation could serve as an effective add-on treatment to heavy slow resistance (HSR) training in the treatment of tendinopathy. This study investigated whether daily hydrolyzed collagen ingestion enhances HSR training outcomes compared with placebo in male elite athletes with chronic patellar, Achilles, or plantar fascia tendinopathy. Materials and Methods Thirty-six elite athletes with chronic tendinopathy were randomized to receive 10 grams of hydrolyzed collagen or placebo (maltodextrin) daily alongside a 12-week HSR program (three weekly sessions). The primary outcome was pain during sport (Numerical Rating Scale, NRS). Secondary outcomes included NRS scores (post-activity, morning, weekly maximum, provocation), function and symptoms (Victorian Institute of Sports Assessment questionnaires [VISA]), and ultrasound morphology (thickness, echogenicity, power Doppler area [PDA]). Assessments were conducted at baseline, 12 weeks, and 38 weeks. Results Both groups demonstrated clinically relevant improvements in NRS during sport after 12 weeks, with sustained effects at 38 weeks (Collagen: baseline 3.90±0.59; 12 weeks 2.20±0.45; 38 weeks 1.50±0.34; Placebo: baseline 5.00±0.45; 12 weeks 2.20±0.28; 38 weeks 2.30±0.57). Secondary outcomes, including other NRS scores and VISA-Patella, improved similarly in both groups. Ultrasound PDA improved after 12 weeks. No significant differences were observed between the collagen and placebo groups for primary or secondary outcomes. Conclusion This study found no superior clinical effect of collagen supplementation as an add-on to HSR training in elite athletes with tendinopathy.
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