Lenny and Larrys
You've probably heard some version of the warning: running too much will eat away at your muscle, or lifting heavy will slow you down on the road. Hybrid training formats built around alternating runs and functional stations, the kind of thing you see in events like HYROX competitions, have put this question back in front of a lot of people who train for general fitness rather than a single sport. So what actually happens inside your body when you ask it to build strength and endurance at the same time, and does one really come at the expense of the other?
Before you begin - always consult your physician before beginning any exercise (or dietary) program(s). This general information is not intended to diagnose any medical condition or to replace your healthcare professional. Consult with your healthcare professional to design an appropriate exercise prescription (or dietary program) that's right for you.
What Happens Inside Your Muscles When You Combine Both Types Of Training
Strength and endurance training send competing chemical signals inside the same muscle fibers. Resistance training turns on a pathway called mTOR, which tells your muscle cells to grow larger and stronger. Endurance training activates a different pathway called AMPK, which tells those same cells to build more mitochondria and become more efficient at using oxygen. Researchers have studied whether activating both pathways close together blunts each one's signal, a phenomenon first documented in Robert Hickson's 1980 study, which found that untrained men gained less strength from combined training than from lifting alone.
Does Cardio Actually Reduce Your Strength Gains
Cardio has a small effect on strength gains, and it depends heavily on who you are. A 2024 systematic review and meta-analysis found that concurrent training produced a small reduction in lower-body strength gains in men, but no meaningful reduction in women at all. The same review found that untrained endurance athletes experienced blunted aerobic improvements when strength work was added, while trained and highly trained endurance athletes did not see that same interference. In other words, the "cardio kills gains" effect is real, but it shows up mostly in specific groups rather than across the board.
Does Strength Training Affect Your Endurance Gains
Lifting weights barely touches your aerobic capacity when both are programmed together. A 2025 umbrella review pulling together seventeen meta-analyses across more than 1,400 participants found that people who trained both strength and endurance together saw aerobic capacity improvements comparable to those who trained endurance alone. If you're worried that adding a lifting program will slow down your running or rowing progress, the aerobic side of the equation holds up well.
What Determines How Much Interference You'll Actually Experience
The type, frequency, and duration of your cardio matter more than the fact that you're doing cardio at all. An earlier meta-analysis found that interference effects scale with how much endurance volume you do, and that running in particular produced more interference on strength and hypertrophy than cycling did, likely because running places more direct mechanical stress and fatigue on the same muscle groups used in lifting. Someone doing two short cycling sessions a week alongside a lifting program is in a very different position than someone marathon training while trying to build maximal strength.
| Factor | Tends To Increase Interference | Tends To Minimize Interference |
|---|---|---|
| Training Status | Untrained or beginner lifters | Trained or highly trained athletes |
| Sex | Men show a small strength interference effect | Women show little to no measurable effect |
| Cardio Modality | Running (higher mechanical overlap with lifting) | Cycling or low-impact cardio |
| Cardio Volume | High frequency, long duration sessions | Moderate, well-managed weekly volume |
Does It Matter Which One You Do First In A Workout
Training order changes short-term muscle signaling but rarely changes your long-term results. A 2025 review of training sequencing found that the order you perform strength and endurance work in generally shows no consistent link to final gains in strength, hypertrophy, or endurance. It did find that a strength-first approach tends to support better neuromuscular output and explosive power in that specific session, which is useful if a workout's main goal is a heavy lift, but this didn't translate into meaningfully different results over time. A separate 2023 meta-analysis on training sequence and lower limb strength reached a similar conclusion. If your schedule or a hybrid race format forces you into a specific order, the research suggests you're not sabotaging your long-term progress either way.
How To Structure Your Training If You Want Both
Most people can build real strength and real endurance at the same time with a few simple adjustments. Based on the patterns in the research, a few practical guidelines hold up:
- Keep weekly cardio volume moderate rather than maximal if strength is a priority, since volume and frequency are the biggest levers on interference.
- Favor lower-impact cardio like cycling, rowing, or incline walking on days close to heavy lower-body lifting, since running appears to create more direct competition for recovery.
- Don't stress too much about which one you do first in a session. Do the one that matters most to you that day, since sequencing has a limited effect on long-term outcomes.
- Give yourself adequate recovery between hard sessions of either type. Total recovery capacity, including sleep and protein intake, plays a bigger role in how well you handle combined training than most people assume.
What This Means If You Train For Something Like Hybrid Racing
Formats that alternate running and strength stations back to back are demanding on recovery, not necessarily on your ability to adapt. Events built around this format ask your body to express both qualities in the same session repeatedly, which is a real training stimulus in its own right rather than a shortcut around the interference conversation. The research above still applies: your weekly structure, your cardio modality choices, and your recovery habits matter more than the specific event format you're training toward.
Recovery capacity also depends on what you're eating around these sessions. Getting enough protein spread across the day, rather than in one large serving, supports the muscle repair work your body is doing on both the strength and endurance side.