L-Threonine Amino Acids: No Muscle Boost for Older Men

observational-study PMID: 12131252

L-Threonine Amino Acids: No Muscle Boost for Older Men

Quick Summary: A study tested if a daily mix of amino acids including L-threonine, plus carbs, could help older men build more muscle strength and size during 12 weeks of leg workouts. Both the supplement group and the no-supplement group improved equally from the exercise alone, with no extra gains from the L-threonine blend. This means the supplement didn't add any real benefit beyond working out.

What the Research Found

Researchers wanted to see if taking amino acids like L-threonine by mouth could supercharge muscle gains in older guys doing strength training. L-Threonine is one of eight essential amino acids in the body that help build proteins, and it's often in supplements for muscle health. But the study showed the mix didn't make a difference.

Key results in simple terms:
- Everyone got stronger and bigger muscles from the workouts, but the supplement group didn't do any better than the group without it.
- Leg strength jumped 21% for holding steady force, and up to 24% for quick movements.
- Max weight lifted (one-rep max) rose 50% in both groups.
- Thigh muscle size grew 6.5% for everyone.
- Muscle power per size improved 12% across the board.

All these changes were real (backed by stats with P < 0.05), but the supplement didn't push them further. In short, exercise did the heavy lifting—L-threonine and friends didn't help extra.

Study Details

Who was studied: 17 healthy older men over age 65 (average around 71 years old). Eight took the supplement; nine did not. They were a mix of weights (75-91 kg) and heights (about 5'10"), but all men—no women included.
How long: 12 weeks of progressive leg workouts, focusing on knee extensions to build strength step by step.
What they took: The supplement group got a daily post-workout drink with 15 grams of eight amino acids (including L-threonine, but exact amount per one not listed) mixed with 30 grams of carbs like sugar for quick energy. The other group got nothing extra—just trained.

They measured strength with machines for steady holds, fast twists, and max lifts, plus scanned thighs with CT scans for muscle size before and after.

What This Means For You

If you're an older man (over 65) looking to get stronger or bigger muscles, this study suggests skipping fancy amino acid supplements with L-threonine. Focus on regular strength training like leg presses or squats— that's what drove the 50% strength boost and 6.5% muscle growth here.

Save your money: These supplements didn't add value, so stick to a balanced diet with enough protein from food (like chicken, eggs, or beans) instead of pills or powders.
Start simple: Aim for 2-3 workout sessions a week with weights you can handle, and build up. No need for extras if you're eating well.
Talk to a doc: If you're low on energy or have health issues, check with your doctor before trying any supplement— this study was on healthy guys only.

Overall, resistance training is your best bet for staying strong as you age, without relying on L-threonine mixes.

Study Limitations

This research isn't perfect, so take it with a grain of salt:
- Small group: Only 17 men total, so it might miss smaller effects that bigger studies could spot.
- Men only: Results might differ for women or younger folks—can't say for sure.
- Combo supplement: L-threonine was mixed with other amino acids and carbs, so we don't know if L-threonine alone would help (or hurt).
- No fake pill: The no-supplement group knew they got nothing, which could affect motivation compared to the supplement takers.
- Short time: 12 weeks is a start, but long-term effects (like over a year) weren't tested.
- Old study: From 2002, so newer research might show different results with better methods.

For the best advice, look at your own health and maybe combine this with other studies on amino acids.

Key Findings

The study concluded that a daily oral supplement containing L-threonine (as part of an 8-amino-acid complex) combined with carbohydrates did not enhance muscle strength or size gains in older men undergoing 12 weeks of resistance training. Both experimental (EX) and control (CN) groups showed significant within-group improvements in all measured outcomes due to training (P < 0.05), but no statistically significant differences existed between groups. Key metrics included:
- Isometric strength: +21% in both groups
- Isokinetic torque: +24% to +11% across velocities (1.05–5.24 rad/s)
- 1RM strength: +50% in both groups
- Thigh cross-sectional area (CSA): +6.5% in both groups
- Voluntary torque/CSA: +12% in both groups (P < 0.05)

Study Design

This was a randomized controlled trial (misclassified as "observational" in the source metadata) with a 12-week duration. Seventeen men aged >65 years (EX: n=8, 70.8±1.5 yr; CN: n=9, 72.1±1.9 yr) completed unilateral knee extensor progressive resistance training. Participants were randomized to EX (amino acids + carbs) or CN (no supplement). Outcomes included isometric/isokinetic torque, work capacity, 1RM strength, and thigh CSA via computed tomography, measured pre- and post-intervention.

Dosage & Administration

The EX group consumed a daily oral supplement providing 15g total amino acids (including L-threonine, L-lysine, L-leucine, L-valine, L-phenylalanine, L-histidine, L-isoleucine, and L-methionine) combined with 30g carbohydrates (dextrose, sucrose, fructose). Doses for individual amino acids (e.g., L-threonine) were not specified in the study. Supplements were administered post-exercise daily throughout the 12-week training period. The CN group received no supplement.

Results & Efficacy

All strength and size metrics improved significantly with training (P < 0.05 within groups), but no inter-group differences were observed. Statistical analysis confirmed no significant effects of the supplement on:
- Isometric torque (P > 0.05 for EX vs. CN)
- Isokinetic torque across all velocities (P > 0.05)
- 1RM strength (P > 0.05)
- Thigh CSA (P > 0.05)
- Torque/CSA ratio (P > 0.05)
Effect sizes (e.g., 21% isometric strength gain) were identical between groups, indicating the amino acid-carbohydrate mix provided no additional benefit beyond resistance training alone.

Limitations

Key limitations include:
- Small sample size (n=17 total), reducing statistical power to detect modest effects.
- L-threonine not isolated: Results reflect an 8-amino-acid blend; L-threonine-specific effects cannot be determined.
- No placebo control: The CN group received no intervention, potentially introducing bias (e.g., expectation effects in EX group).
- Homogeneous cohort: Only older men were studied; findings may not generalize to women, younger adults, or clinical populations.
- Unreported individual amino acid doses: Prevents replication or assessment of L-threonine’s role.
- Short duration: 12 weeks may be insufficient to observe long-term adaptations.

Clinical Relevance

For older men using L-threonine-containing supplements, this study indicates no measurable benefit for muscle hypertrophy or strength when combined with resistance training. The identical gains in both groups (e.g., +6.5% CSA, +50% 1RM) suggest that prioritizing adequate total protein intake and consistent resistance training is more impactful than adding this specific amino acid-carbohydrate formulation. Consumers should be cautious about claims for multi-amino-acid blends in aging populations, as this evidence shows they do not augment training adaptations beyond exercise alone. Future research should isolate individual amino acids like L-threonine at defined doses.