Peptide hormones and exercise are tightly linked: a workout is, after sleep, the strongest natural trigger for growth hormone release, and a single session shifts appetite hormones, lowering hunger-promoting acylated ghrelin by a median 16.5% and raising fullness hormones by about 9-15%.[1][2] Exercise also raises muscle and mitochondrial peptides such as irisin, MOTS-c and humanin, though what these do in people is still being worked out.[4][5][6]

This page reviews the key studies, separates the solid findings from the speculative ones, and explains where peptide drugs fit in sport. For related compounds, see our muscle and metabolism peptides hub.

Bottom line

HormoneWhat exercise doesStrength of evidence
Growth hormoneRises sharply, especially above the lactate threshold[1]Strong
Acylated ghrelin (hunger)Falls, median 16.5% after one session[2]Moderate
PYY, GLP-1, pancreatic polypeptide (fullness)Rise, median 9-15%[2]Moderate
IrisinRises modestly with aerobic interval training[4]Moderate that it rises; weak on effects
MOTS-cRises about 12-fold in muscle after cycling[5]Small studies
HumaninRises in muscle and blood after interval exercise[6]Small studies

Growth hormone: the classic exercise peptide

Growth hormone (GH) is released in pulses, mostly during sleep. Exercise is the most powerful trigger outside of sleep.[1]

Key findings from a review of exercise and GH:[1]

  • Intensity matters. Exercise above the lactate threshold (the point where breathing gets hard and lactate builds up) for at least about 10 minutes produces the biggest rise.
  • Resistance training works too, with load and frequency affecting the size of the response.
  • Possible triggers include nerve signals from working muscles, lactate and nitric oxide.
  • Trained athletes respond differently. Endurance training may lower resting GH and blunt the post-exercise spike, perhaps because tissues become more sensitive to it.

A key caveat: the short-lived GH spike after a workout isn’t the main driver of muscle growth. Much of the muscle-building signal is attributed to IGF-1, a growth factor produced in response to GH, along with local factors in the muscle.[1]

Appetite hormones

A 2014 meta-analysis pooled 20 studies (28 trials, 241 participants) measuring gut hormones during and after a single exercise session.[2]

  • Acylated ghrelin, the active form of the “hunger hormone,” fell by a median 16.5%.
  • PYY rose by a median 8.9%, GLP-1 by 13% and pancreatic polypeptide by 15%. These hormones signal fullness.
  • The effects were small to moderate, and the authors detected publication bias, meaning studies with positive results may be overrepresented.

GLP-1 is the same hormone that drugs like semaglutide mimic, but at vastly higher and longer-lasting levels than exercise produces. Exercise’s effect is brief and modest by comparison.

Myokines and mitochondrial peptides

Irisin. Discovered in mice in 2012, irisin is released from muscle during exercise and was shown to turn white fat into calorie-burning “brown-like” fat in mice.[3] Its existence in humans was questioned because of unreliable antibody tests. A 2015 mass spectrometry study settled that debate: irisin circulates at about 3.6 ng/mL in sedentary people and about 4.3 ng/mL in people doing aerobic interval training.[4] Whether those levels meaningfully affect human fat or metabolism remains uncertain.

MOTS-c. In 10 young men, a cycling session raised MOTS-c about 12-fold in muscle and modestly in blood. In mice, MOTS-c treatment improved running capacity at all ages.[5]

Humanin. A session of high-intensity interval cycling raised humanin in the muscle and blood of young men.[6]

These findings suggest that some of exercise’s benefits may be carried by peptide signals. But no study has shown that injecting MOTS-c or humanin reproduces the benefits of exercise in people. Our mitochondrial peptides research page covers their evidence in detail.

Can peptide drugs replace or boost training?

The best test comes from growth hormone. In a randomized, placebo-controlled trial, 96 recreationally trained athletes took GH (2 mg a day), testosterone, both, or placebo for 8 weeks.[7]

  • GH cut fat mass and raised lean body mass, but mainly through extra body water.
  • Sprint capacity rose by about 3.9% with GH alone, and 8.3% in men taking GH plus testosterone.
  • Strength, power and endurance did not improve.
  • The sprint gain disappeared within 6 weeks of stopping.

The authors noted that doses used covertly by athletes may be higher and that the trial was too small to judge safety.[7] See our human growth hormone profile and our peptides vs HGH comparison for more.

Established vs preliminary

Established:

  • Exercise stimulates GH release, scaled by intensity.[1]
  • A single exercise session modestly lowers ghrelin and raises fullness hormones.[2]
  • Irisin is a real circulating human peptide that rises with training.[4]

Preliminary:

  • Whether exercise-induced myokines explain the health benefits of exercise.
  • Long-term effects of training on appetite hormones and food intake.
  • Any benefit from injecting exercise-related peptides.

Limitations

  • Short studies. Most appetite-hormone research measures a few hours after one session.[2]
  • Small samples. The MOTS-c and humanin exercise studies included about 10 people each.[5][6]
  • Measurement problems. Early irisin research relied on antibody kits that later proved unreliable.[4]

Peptide hormones in sport

WADA’s 2026 Prohibited List bans peptide hormones, growth factors and related substances at all times. This includes growth hormone, GH-releasing hormones and secretagogues such as ipamorelin, IGF-1 and mechano growth factors. MOTS-c is separately banned as a metabolic modulator.[8] Our WADA peptide list guide explains the categories, and follistatin and myostatin research covers a newer class of muscle-targeting drugs.

For everyone else, the takeaway is simple: training already triggers a rich hormonal response. Talk with a clinician before considering any peptide product marketed to “boost” it.