Optimizing Velocity Loss for Endurance Athlete Strength Training

Concurrent Training: The Science of Strength, Endurance, and Fatigue Management

A comprehensive Spanish-Brazilian study has found that the fatigue you allow during resistance training directly controls the outcomes of a combined strength and endurance program. Research from the Universidad Pablo de Olavide and the Nucleus of High Performance in Sport in São Paulo reveals that managing “velocity loss” in the gym is a key tool for endurance athletes who lift weights.

Velocity Loss is Your Adaptation Control Knob

The 2026 study led by Tundidor-Duque and Pareja-Blanco assigned 41 moderately trained men to different 8-week programs. The critical variable was “velocity loss” (VL) during squat sessions. One group stopped their sets the moment bar speed dropped by 15% from the first rep (VL15). Another trained to a 40% velocity loss (VL40), a point of significant fatigue. A third group performed each rep at peak speed with no loss (VL0). All strength groups then performed high-intensity running after a 10-minute rest.

Results showed this technical variable controlled the adaptation roadmap. The VL40 group achieved the greatest gains in muscle cross-sectional area. However, for improvements in maximal aerobic speed (MAS)—a key endurance metric—the trend reversed. The lower the velocity loss, the higher the effect size for aerobic gains. VL0 saw the best endurance improvements from concurrent training, though the endurance-only group improved MAS the most. This creates a clear trade-off: more fatigue drives hypertrophy, but less fatigue better preserves the neuromuscular state needed for optimal endurance adaptation.

Endurance Training Can Weaken the Neuromuscular System

A striking finding was the negative impact of endurance-only training on strength metrics. While the endurance group improved aerobic capacity, they showed no strength gains and significantly reduced their rate of force development at 400 milliseconds. Electromyography (EMG) data showed reduced muscle activation amplitude. “ET enhanced aerobic performance but impaired neuromuscular function,” the authors concluded.

This impairment may relate to the specific demands of prolonged high-intensity running, which could promote neuromuscular fatigue patterns that conflict with explosive force production. It highlights a potential pitfall for dedicated endurance athletes: without resistance training, they risk losing power and muscular coordination. This supports the premise of concurrent training as a time-efficient path to comprehensive fitness, protecting against the downsides of a single-mode approach.

Designing Your Concurrent Training Program

How do you apply this? First, define your priority. Is your main goal a faster 10k time or greater overall athletic performance? For endurance athletes, the research suggests adopting a low-fatigue resistance model. Use a velocity-based tracker or the “repetitions in reserve” method, stopping sets well before muscular failure—perhaps at a 15-20% velocity loss or with 2-3 reps left in the tank. This preserves your nervous system for the quality running that follows.

If your goal is balanced fitness or muscle growth alongside endurance, a moderate VL (15-25%) is effective. The study’s VL15 group increased their one-repetition maximum (1RM) and improved strength variables without sacrificing as much endurance potential as the VL40 group. The protocol itself was manageable: two sessions per week, with squats at 70-85% of 1RM followed by running at 90-105% of maximal aerobic speed after a short break. This order—strength before endurance—is supported by the narrative review co-authored by Loturco, which notes it helps maintain the quality of the technically demanding resistance work.

Frequently Asked Questions

Can I do my strength and endurance workouts on the same day?

Yes, the study used this model successfully. The key is separating the sessions by at least 10 minutes of rest to allow for partial recovery, and performing the strength portion first to ensure good technique and intensity.

If I’m only interested in endurance, should I avoid lifting heavy weights?

No. The endurance-only group lost neuromuscular function. Incorporating low-fatigue strength training (low velocity loss) protects your power and force production, which can improve running economy and prevent injury, without harming your endurance gains.

How do I measure “velocity loss” without high-tech gear?

While velocity-based training devices are precise, you can approximate it by focusing on bar speed. Stop your set as soon as your reps noticeably slow down. Using a “repetitions in reserve” (RIR) target of 2-3 is a practical alternative that aligns with low velocity loss.

Does this apply to low-intensity Zone 2 training as well?

The study used high-intensity running, but the principle likely holds. Fatigue from heavy resistance work could compromise the muscular coordination and mitochondrial signaling benefits of any subsequent endurance work, whether low or high intensity. Managing fatigue in the weight room remains prudent.

Sources:
https://pubmed.ncbi.nlm.nih.gov/41855389/
https://pubmed.ncbi.nlm.nih.gov/41766799/
https://pubmed.ncbi.nlm.nih.gov/41762427/