Why Most Training Programs Get It Wrong

Most training programs are built around one thing.

Powerlifting programs are built around the squat, bench, and deadlift. Bodybuilding programs are built around maximizing muscle size. CrossFit is built around conditioning and competition. Running programs are built around mileage and pace.

If you’re a competitive athlete, that makes sense. You pick the thing you want to be great at and you go all in.

But most people reading this aren’t competitive athletes. Most people just want to be strong, look good, have energy, and not fall apart at 55. And for that, specializing in one fitness quality is the wrong approach.

The Specialization Problem

A program that only builds muscle doesn’t protect your heart. A program that only builds endurance doesn’t protect your bones or keep you strong enough to pick up your kids without thinking about it. A program that only builds strength doesn’t keep you from getting winded walking up stairs.

You need all of it. Strength, muscle, cardiovascular fitness, the ability to move well and recover quickly.

Not one maximized and the rest ignored.

The training world has been slow to accept this because it’s easier to market a single focus. “Get jacked.” “Run a marathon.” “Hit a 500lb deadlift.” Clear, simple, sellable. But for anyone whose goal is just to be a capable, healthy human being for a long time, single-focus programs leave massive gaps.

The fix is something called concurrent training.

What Concurrent Training Is

Concurrent training means training multiple fitness qualities in the same session (sometimes called same-session concurrent training in exercise science literature). Strength, muscle, and conditioning. All in one workout.

Not separate days. Not separate training blocks. Every session covers all of it.

A typical concurrent session looks something like this: a main compound lift trained for strength, accessory work trained for muscle, then 7-20 minutes of conditioning to finish. Total session time: about 50-60 minutes.

This is the opposite of how most programs are designed. Most programs dedicate entire sessions (or even entire weeks) to one quality at a time. Monday is chest day. Tuesday is cardio. Legs on Thursday. You know the drill.

Concurrent training throws that out. You train the whole system every time you walk in the gym.

“But Doesn’t Cardio Kill Your Gains?”

This is the most common pushback, and it’s based on outdated science.

The idea of the “interference effect” comes from research in the 1980s where subjects ran for 45+ minutes and then tried to build muscle. That combination did cause problems. But that’s a terrible comparison to 10-15 minutes of structured conditioning after lifting.

The modern research tells a completely different story.

A 2022 meta-analysis in Sports Medicine looked at 43 studies comparing strength training alone versus strength training combined with conditioning. Adding conditioning had essentially zero effect on muscle growth. The standardized effect on hypertrophy was -0.01. Statistically nothing. Maximal strength wasn’t meaningfully affected either. The only slight reduction was in explosive power output, which matters for Olympic lifters and sprinters. Not for people training to stay healthy.

A 2024 study in the Journal of Human Kinetics tested resistance-trained men doing strength plus high-intensity cycling in the same session versus strength alone. No difference in lower body strength gains. No difference in quad growth. The researchers actually noted that high-intensity interval conditioning may reduce interference because it shares similar neuromuscular demands with lifting.

A 2017 study in the Scandinavian Journal of Medicine & Science in Sports had one group do resistance training alone and another do resistance training followed immediately by high-intensity interval cycling. After 8 weeks: both groups gained the same muscle, both gained the same strength, and the concurrent group also improved their aerobic capacity. The strength-only group didn’t.

Same muscle. Same strength. Better cardiovascular fitness.

The fear that conditioning kills your gains doesn’t hold up when the conditioning is short, intense, and placed after your lifting. That’s what the science says.

Why Conditioning Can’t Be Optional

A lot of programs treat conditioning like a bonus. Something you do if you have extra time. Something “for the people who care about that sort of thing.”

That’s a mistake, and the research on this is uncomfortable for anyone who only lifts.

The CardioRACE Trial was published in the European Heart Journal in January 2024. It’s one of the largest and most rigorous studies on combined training. 406 overweight or obese adults aged 35-70 were randomly assigned to aerobic exercise only, resistance training only, combined training, or no exercise. They trained three times per week for one full year under supervision.

After one year: the combined group and the aerobic-only group both showed significant reductions in cardiovascular disease risk factors. Blood pressure, LDL cholesterol, fasting glucose, body fat. All improved.

The resistance-only group did not get the same cardiovascular protection.

Strength training alone was not enough.

A meta-analysis in the European Journal of Preventive Cardiology found resistance training alone was associated with a 21% reduction in all-cause mortality. But when combined with aerobic exercise, that jumped to 40%. Nearly double.

A 2024 study from South Korea tracking nearly 35,000 adults over 9 years found that people meeting both aerobic and muscle-strengthening guidelines had the lowest risk of death from any cause and from cardiovascular disease. Not one or the other. Both.

If you’re lifting but never conditioning, you’re leaving half the benefit on the table. Your muscles don’t mean much if your heart can’t keep up.

The Longevity Data

This is where it gets hard to argue against.

Cardiorespiratory fitness (your body’s ability to transport and use oxygen during sustained effort) is one of the single strongest predictors of how long you live. Stronger than blood pressure. Stronger than cholesterol. Stronger than BMI.

A study in JAMA Network Open followed over 122,000 patients and found that low cardiorespiratory fitness carried a higher mortality risk than smoking, diabetes, or hypertension. Being unfit was more dangerous than being a smoker.

A 46-year study from Copenhagen published in the Journal of the American College of Cardiology found that each 1 ml/kg/min increase in VO2max was associated with a 45-day increase in lifespan. People in the highest fitness category lived nearly 5 years longer than those in the lowest.

Pair that with the strength data. Research from the Journal of the American Heart Association showed that women doing both strength training and 150+ minutes of aerobic activity per week had the lowest mortality risk of any group studied. Strength alone helped. Conditioning alone helped. Both together was the clear winner.

A review in Mayo Clinic Proceedings concluded that the ideal exercise pattern is moderate to vigorous aerobic activity combined with strength training. The review specifically noted that HIIT-style conditioning (short, intense bursts) is one of the most efficient ways to build and maintain high cardiorespiratory fitness without the joint stress of long endurance sessions.

You don’t need to run marathons. You don’t need 45-minute treadmill sessions. You need short, hard conditioning consistently alongside your strength work. That’s what the evidence points to over and over.

What the WHO and CDC Actually Recommend

The WHO’s 2020 Physical Activity Guidelines recommend that all adults get 150-300 minutes of moderate aerobic activity (or 75-150 minutes of vigorous activity) per week, plus muscle-strengthening activities on 2 or more days per week.

The WHO specifically states you can “combine all types of exercise (aerobic, muscle strengthening, and balance training) into a session, and this has been shown to be effective.”

The CDC recommends the same.

Only about 23% of American adults meet both guidelines. Most people either lift and skip conditioning, or do cardio and skip strength. Concurrent training solves that automatically.

Concurrent vs. Hybrid: Two Valid Approaches

If the research supports training both qualities, the obvious question is: does it matter if you do them in the same session or on separate days?

The “hybrid” approach (known in the research as separate-session concurrent training, where strength and conditioning get their own dedicated days) is popular right now. And it works. You can absolutely get strong and fit splitting them up.

But concurrent training has a structural advantage: you never skip one modality. If you train 3 days this week instead of 5, you still got strength and conditioning in every session. With a hybrid setup, miss your conditioning days and you only lifted. Miss your lifting days and you only did cardio.

Concurrent training also tends to be more time-efficient. Five 50-60 minute sessions covering both modalities versus 3 strength sessions and 2-3 separate cardio sessions. Same total work in fewer trips to the gym.

Both approaches are valid. But for people who want a simple, reliable structure where nothing gets neglected no matter how the week goes, concurrent is hard to beat.

So What Does Good Concurrent Training Look Like?

This is where most people get stuck. The research is clear that concurrent training works. But putting together a well-structured concurrent program is harder than just doing push/pull/legs and adding a run at the end.

A good concurrent program needs to:

Prioritize strength work first, when you’re fresh and technique matters most. Place conditioning after, where metabolic work is less precision-dependent. Manage total volume so recovery doesn’t become the bottleneck. Rotate exercises to prevent overuse and keep adaptation happening. Use intensity controls so you’re not accidentally redlining every session.

That’s a lot to figure out on your own. It’s also exactly what the FLEX program was built to do.

How FLEX Does It

FLEX is a concurrent training program that runs on a 5-day split through a custom app. Every session combines strength, hypertrophy, and conditioning.

Day 1 pairs a squatting movement with a pulling movement, plus conditioning.

Day 2 pairs a hinging movement with a pushing movement, plus conditioning.

Day 3 is dedicated core work followed by conditioning.

Day 4 is lower body volume work. Accessory movements, structural balance, single-leg work, plus conditioning.

Day 5 is upper body volume work. Accessory movements, isolation work, plus conditioning.

Exercises rotate every 6 weeks. Loading is RPE-based so you adjust to how you feel on any given day. Conditioning varies between AMRAPs, EMOMs, intervals, and for-time pieces, with intensity cues telling you exactly how hard to push.

The structure means that even if you only train 3 or 4 days in a given week, you’re still getting full-body coverage with conditioning built in. Nothing gets skipped.

Two tracks are available: Full Gym (barbells, dumbbells, cables, standard equipment) and Minimal (dumbbells only). Both follow the same programming principles. Neither is a watered-down version.

FLEX isn’t a bodybuilding program. It won’t maximize muscle size the way a pure hypertrophy program would. It isn’t CrossFit. It won’t develop conditioning the way daily metcons would. It isn’t a powerlifting program. It won’t push your competition lifts as high as dedicated peaking cycles would.

It accepts those trade-offs because for people who aren’t competing in any of those sports, training everything at once is the better play. The research backs that up. The health outcomes back that up. The longevity data backs that up.

The Science at a Glance

What the Research Shows	Source
Adding conditioning to strength training has zero effect on muscle growth	Schumann et al., Sports Medicine, 2022. Meta-analysis of 43 studies (link)
Combined training reduces cardiovascular disease risk as much as aerobic-only training	CardioRACE Trial, European Heart Journal, 2024. 406 adults, 1 year (link)
Resistance + aerobic exercise = 40% lower all-cause mortality vs. 21% for resistance alone	Saeidifard et al., European Journal of Preventive Cardiology, 2019 (link)
Each 1 ml/kg/min increase in VO2max = 45 extra days of life	Eriksen et al., Journal of the American College of Cardiology, 2018. 46 years follow-up (link)
Low cardiorespiratory fitness carries higher mortality risk than smoking, diabetes, or hypertension	Mandsager et al., JAMA Network Open, 2018. 122,007 patients (link)
Same-session HIIT after strength training does not reduce muscle or strength gains	Tsitkanou et al., Scand J Med Sci Sports, 2017 (link)
Meeting both aerobic + strength guidelines = lowest mortality risk	Jeong et al., Hypertension Research, 2024. 34,990 adults, 9 years (link)
Concurrent training superior to endurance-only for blood pressure and body composition	López-Ruiz et al., Scientific Reports, 2025. 75 adults, 12 weeks (link)
Concurrent training effective for both strength and cardiorespiratory fitness in middle-aged and older adults	Markov et al., Sports Medicine, 2023. Systematic review and meta-analysis (link)
Strength training associated with 27% lower mortality risk in women; combined with aerobic = lowest risk	Shiroma et al., Journal of the American Heart Association, 2017. 28,879 women (link)
WHO endorses combining strength, aerobic, and balance training in single sessions	WHO Physical Activity Guidelines, 2020 (link)

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