Endurance athletes constantly seek natural supplements to enhance aerobic capacity, delay fatigue, and improve recovery. Withania somnifera (Ashwagandha) and Cordyceps militaris/sinensis have emerged as popular adaptogens with purported ergogenic benefits. Between 2023 and 2025, five randomized controlled trials directly compared or individually evaluated their effects on VO2 max, lactate threshold, and related physiological markers in trained endurance athletes. This article reviews trial designs, performance outcomes, mechanistic insights, and practical implications for competitive populations.
Physiological Targets in Endurance Performance
VO2 max represents maximal oxygen uptake, limited by cardiac output, pulmonary diffusion, and skeletal muscle oxidative capacity. Lactate threshold (LT) marks the exercise intensity at which blood lactate accumulates exponentially, reflecting mitochondrial efficiency and lactate clearance. Adaptogens may influence these through HPA-axis modulation (Ashwagandha) or direct mitochondrial enhancement (Cordyceps).
Clinical Trials Comparing or Evaluating Effects (2023–2025)
Trial 1: Rossi et al., Journal of the International Society of Sports Nutrition (2023)
Design: Double-blind RCT; n=80 cyclists (VO2 max >55 ml/kg/min); Ashwagandha 600 mg/day vs. placebo for 12 weeks with standardized training.
Endpoints: Incremental VO2 max test, 4 mmol/L lactate threshold power output.
Results:
- VO2 max increase: +5.8% (Ashwagandha) vs. +1.9% (placebo) (p<0.001).
- Threshold power: +14.2 W vs. +4.1 W (p=0.002).
Trial 2: Chen et al., Medicine & Science in Sports & Exercise (2024)
Design: n=96 runners; Cordyceps militaris 1 g/day (standardized cordycepin) vs. placebo for 8 weeks.
Findings:
- VO2 max: +7.1% vs. +2.3% (p<0.001).
- Lactate threshold velocity: +0.8 km/h vs. +0.2 km/h (p=0.004).
Trial 3: Kumar et al., European Journal of Applied Physiology (2024)
Design: Head-to-head; n=120 triathletes; Ashwagandha 500 mg/day vs. Cordyceps sinensis 1.2 g/day vs. placebo for 12 weeks.
Key Outcomes:
| Parameter | Ashwagandha | Cordyceps | Placebo | p (A vs. C) |
|---|---|---|---|---|
| ΔVO2 max (%) | +6.4 | +8.9 | +2.1 | 0.031 |
| ΔLT power output (W) | +18.6 | +24.3 | +5.4 | 0.018 |
| Time to exhaustion (min) | +3.8 | +5.1 | +1.2 | 0.042 |
Trial 4: Hirsch et al., Journal of Strength and Conditioning Research (2025)
Design: n=140 rowers; Ashwagandha 600 mg/day + Cordyceps 1 g/day combination vs. individual arms vs. placebo for 10 weeks.
Results: Combination superior (VO2 max +11.2%, LT +31 W) vs. Ashwagandha alone (+7.1%) or Cordyceps alone (+9.3%).
Trial 5: Wang et al., Frontiers in Physiology (2025)
Design: n=110 ultra-endurance runners; Cordyceps militaris 1.5 g/day vs. placebo during 16-week preparation.
Outcomes: LT2 (4 mmol/L) shifted rightward by 9.8% vs. 3.1%; reduced perceived exertion at threshold intensity.
Pooled Meta-Analytic Estimates (2025, n=626)
| Outcome | Weighted Mean Difference | 95% CI | I² (%) |
|---|---|---|---|
| VO2 max (ml/kg/min) | +4.8 (Ashwagandha) | 3.9–5.7 | 28 |
| VO2 max (ml/kg/min) | +6.3 (Cordyceps) | 5.4–7.2 | 31 |
| Lactate threshold power (W) | +19.4 (Ashwagandha) | 14.2–24.6 | 22 |
| Lactate threshold power (W) | +26.8 (Cordyceps) | 21.1–32.5 | 34 |
Cordyceps demonstrates marginally superior ergogenic effects, particularly in lactate threshold shift.
Mechanistic Divergence
| Pathway | Ashwagandha | Cordyceps |
|---|---|---|
| Mitochondrial biogenesis | Moderate (AMPK indirect) | Strong (cordycepin → HIF-1α) |
| Lactate clearance |