DO HYBRID ATHLETES NEED MORE PROTEIN? WHAT THE STUDIES MEASURED

A lot of hybrid-training content says that training strength and endurance together means you need more protein than a lifter or a runner. Chapter 8 of The Hybrid Athlete Protocol looked for research establishing that and couldn't find it. Here's what the concurrent-training protein studies did measure, including a randomized trial in women aged 40 to 77 published September 14, 2026.

The Systematic Review: What Protein Changed and What It Didn't

In 2022, Hartono and colleagues published a systematic review in Sports Medicine on protein supplementation during concurrent resistance and endurance training in healthy adults aged 18 to 65.

• Short-term: four acute studies, all in 84 trained young men, found that protein after a concurrent session raised myofibrillar protein synthesis (building contractile muscle tissue) but not mitochondrial protein synthesis (tied to endurance adaptation).
• Muscle mass: five of nine longer-term studies reported that protein enhanced gains.
• Strength or power: five of nine reported enhanced gains.
• Aerobic capacity: all six studies that measured VO2max found no effect of added protein.

The authors described this as "some evidence" for mass and strength/power, and none for whole-body aerobic capacity. In short, protein was associated with the strength side of the adaptation, not the endurance side.

Two Trials That Assigned Protein Targets Directly

A supplement study asks whether adding protein helps. A more direct test of "do hybrid athletes need more" is to assign different daily targets to people doing concurrent training and compare results. One research group has done that twice.

Young trained men, 2023. In a trial in the Journal of the International Society of Sports Nutrition, Bagheri and colleagues assigned 48 resistance-trained men (average age 26) to 16 weeks of resistance training alone or resistance plus endurance training, eating either 1.6 or 3.2 grams of protein per kilogram of bodyweight per day. Performance, lean mass, strength, and power improved in all four groups, and VO2max rose in both concurrent groups. The one outcome that differed was peak power, which improved more in the resistance-only 3.2 g/kg group than in the two 1.6 g/kg groups. The authors concluded that, apart from peak power, 1.6 g/kg appeared sufficient in both training types in young, healthy adults.

Middle-aged and older women, 2026. Published online September 14, 2026, in the same journal, a 2×3 factorial trial randomized 108 women aged 40 to 77 to 12 weeks of supervised resistance training or the same program plus cycling, at 0.8, 1.6, or 2.2 g/kg per day. The analysis included 83 women who completed it. For skeletal muscle mass, measured by bioelectrical impedance, there was no effect of protein target and no interaction between protein target and training type. No protein effects were detected on the key secondary outcomes either.

The authors added two limits. Because the concurrent group did more total exercise, differences between training groups can't be attributed to modality alone. And a null result "does not establish equivalence among doses," meaning not finding a difference isn't proof that there isn't one.

What the Kidney and Liver Markers Showed

A companion analysis of the same trial in the European Journal of Nutrition reported that urea, creatinine, and cystatin C rose and estimated kidney function (eGFR) fell, mainly between the 0.8 g/kg group and the two higher-protein groups, with little difference between 1.6 and 2.2. Some liver enzymes also differed by protein condition. The authors stated these changes do not establish organ injury or long-term safety, and that the study couldn't isolate protein dose because diets weren't fully matched.

What the Evidence Doesn't Cover

The Hartono review stops at age 65, and its mechanistic studies were all in young men. The 2023 trial was in men averaging 26. The 2026 trial is the closest to this audience, but it studied women who were supervised for 12 weeks and measured muscle mass with bioelectrical impedance, not scans. I could not find a trial in men over 50, or in trained masters athletes of either sex, comparing protein targets during concurrent training.

The Protocol

How Chapter 8 handles protein for a two-system week:

• The book uses an evidence-based protein intake matched to your training load, body size, and goals, and doesn't raise it just because endurance work is also in the week.
• Protein stays fairly steady across the week. Carbohydrate is what the book adjusts, with more around the hardest endurance and format-specific days.
• If you're unsure your current intake is adequate, the book's advice is to check with a registered dietitian rather than guess.

If you have kidney disease, have been told to limit protein, or take medication that affects kidney function, talk with your physician before changing your protein intake.

Battle Hard. — Will Power

Sources

1. Hartono FA, Martin-Arrowsmith PW, Peeters WM, Churchward-Venne TA. The effects of dietary protein supplementation on acute changes in muscle protein synthesis and longer-term changes in muscle mass, strength, and aerobic capacity in response to concurrent resistance and endurance exercise in healthy adults: a systematic review. Sports Med. 2022;52(6):1295-1328. PMID 35113389
2. Bagheri R, Kargarfard M, Sadeghi R, Scott D, Camera DM. Effects of 16 weeks of two different high-protein diets with either resistance or concurrent training on body composition, muscular strength and performance, and markers of liver and kidney function in resistance-trained males. J Int Soc Sports Nutr. 2023;20(1):2236053. PMID 37516903
3. Bagheri R, Ghobadi H, Mansordehghan M, Camera DM, Kargarfard M. Resistance versus concurrent training with three assigned protein targets in middle-aged and older women: a randomized 2 × 3 factorial trial. J Int Soc Sports Nutr. 2026;23(1):2720742. PMID 42735207
4. Bagheri R, Ghobadi H, Kargarfard M, Suzuki K. Effects of 12 weeks of resistance and concurrent training with graded protein intakes on lipid profile, kidney and liver biomarkers in middle-aged to older women. Eur J Nutr. 2026;65(7):253. PMID 42742755