Training

In 1980, Robert Hickson published the first study showing that combining strength and endurance training simultaneously produced inferior strength gains compared to strength training alone. This "interference effect" has haunted concurrent training ever since, leading many endurance athletes to avoid the weight room entirely and many strength athletes to avoid cardio. But four decades of subsequent research have shown that the interference effect is highly dependent on programming variables — and with intelligent design, it can be minimised to near-zero while capturing the benefits of both modalities.

A 2012 meta-analysis in Sports Medicine concluded that concurrent training does reduce maximal strength gains by approximately 10–15% compared to strength-only training, but has minimal effect on aerobic capacity when endurance volume is held constant. For endurance athletes, this is actually excellent news: you sacrifice a small amount of maximal strength (which is not your primary performance driver) while gaining running economy improvements of 2–8%, injury resilience, and the neuromuscular benefits that pure endurance training cannot provide.

Understanding the Molecular Interference

The interference effect operates at the molecular level through competing signalling pathways. Resistance training activates the mTOR pathway, which drives muscle protein synthesis and hypertrophy. Endurance training activates AMPK, which promotes mitochondrial biogenesis and fat oxidation. The problem: AMPK directly inhibits mTOR. When both pathways are activated simultaneously (e.g., a long run immediately after a strength session), the AMPK signal suppresses the mTOR-driven protein synthesis response by 30–50%.

This molecular conflict has three practical implications for programming:

• Separation matters: Allow at least 6 hours between strength and endurance sessions to minimise AMPK-mTOR cross-talk. If same-day sessions are unavoidable, perform the priority session first.
• Volume matters: High-volume endurance training (15+ hours per week) amplifies AMPK activation chronically, creating a persistent anti-anabolic environment. At moderate endurance volumes (6–10 hours per week), the interference is minimal.
• Type of endurance matters: High-intensity endurance work (intervals, tempo runs) generates greater AMPK activation than Zone 2 training. Scheduling strength sessions on the same day as easy runs — not interval days — reduces molecular interference.

Optimal Weekly Structure for Concurrent Training

The following weekly template minimises interference while maximising the benefits of both modalities. It is designed for an endurance athlete (runner, cyclist, or triathlete) training 6–10 hours per week who wants to add 2 strength sessions:

• Monday: AM — Hard run (intervals or tempo). PM — Rest.
• Tuesday: AM — Easy run (Zone 2, 45–60 min). PM — Strength Session A (lower body power: squats, deadlifts, plyometrics).
• Wednesday: Rest or easy cross-training.
• Thursday: AM — Hard run (threshold or VO2 max intervals). PM — Rest.
• Friday: AM — Easy run (Zone 2, 30–45 min). PM — Strength Session B (posterior chain + stability: hip thrusts, RDLs, single-leg work).
• Saturday: Long run (Zone 2, 90–150 min). No strength.
• Sunday: Rest.

Key principle: strength sessions follow easy days, never hard running days. Hard running + strength on the same day amplifies AMPK, maximises fatigue, and compromises both the next day's training and the strength adaptation. Conversely, easy running before strength does not meaningfully elevate AMPK and serves as an effective warm-up for the lift.

Periodising Strength Within an Endurance Season

Strength training intensity and volume should vary across the annual training cycle to complement — not compete with — endurance periodisation:

• Off-season (4–8 weeks): Highest strength volume. 3 sessions per week, 3–4 sets of 8–12 reps at 65–75% 1RM. This is the one phase where mild hypertrophy is acceptable — building a structural base for the season ahead.
• Base phase (8–12 weeks): 2 sessions per week. Transition to heavier loads, lower reps: 3 × 5 at 80–85% 1RM. The goal shifts from muscle building to neural adaptation — producing more force without adding mass.
• Build/race phase (8–16 weeks): 1–2 sessions per week. Maintenance loading: 2 × 5 at 75–80% 1RM. Volume is intentionally reduced to free recovery capacity for race-specific endurance training. Losing 30% of gym volume maintains 90% of strength gains.
• Taper (2–3 weeks): 1 session per week or none. If lifting during taper, keep loads moderate (70% 1RM) and volume minimal (2 × 3). The last strength session should be 10–14 days before the A-race.

Nutrition for Concurrent Training

Concurrent training demands higher total energy intake than either modality alone. The dual demands of glycogen resynthesis (for endurance) and muscle protein synthesis (for strength) require strategic nutrient timing:

• Daily carbohydrate: 5–8g per kg body weight on double-session days. This supports glycogen resynthesis between the AM run and PM lift, and post-lift replenishment for the next morning's run.
• Daily protein: 1.6–2.0g per kg body weight, distributed across 4–5 meals (0.3–0.4g/kg per meal). The higher end is warranted on strength days to maximise the MPS response despite AMPK competition.
• Post-endurance session: 1.0g/kg carbohydrate + 0.3g/kg protein within 60 minutes. This initiates glycogen resynthesis before the PM strength session.
• Post-strength session: 0.3–0.4g/kg protein + 0.5g/kg carbohydrate within 30 minutes. Prioritise protein to capture the post-lift MPS window.

On double-session days, a NorthLine gel between the morning run and afternoon lift provides fast carbohydrate to begin glycogen replenishment without the heavy digestion of a full meal. Plan your concurrent-training nutrition with the Race Day Nutrition Planner, which calculates macro targets for each session and the optimal timing between them.