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The most prominent female fitness trends of 2025-26 are heavily hormone-focused. Most take something biologically true — estrogen fluctuates, cortisol rises during exercise, fibre type differs slightly between sexes — and build a training recommendation on it that the outcome data doesn't support. In this episode, Dr. Lauren Colenso-Semple evaluates those claims against the actual research.
Dr. Lauren Colenso-Semple completed her PhD at McMaster University under Professor Stuart Phillips, with research focused on strength and performance across the menstrual cycle.
In this episode, Dr. Colenso-Semple explains:
How cycle syncing originated — from rodent ovariectomy studies involving full hormone shutdown to a large extrapolated jump into popular fitness content, and why reducing training volume to align with cycle phase conflicts with what the research shows about long-term volume-dependent adaptation.
Why sex differences in muscle fibre type are very small in untrained people, adaptive with training, and secondary to athlete calibre — and why mitochondrial adaptations are a function of training status rather than sex or age.
Why mechanical tension, achievable across a wide rep range, is the primary driver of muscle growth — and why this holds in men and women of all ages and training backgrounds.
The distinction between Cushing's syndrome, a clinical condition involving chronic cortisol dysregulation, and the normal acute cortisol fluctuations that occur during exercise — and why conflating the two has led to widespread unnecessary concern.
Why the kisspeptin argument against fasted training for women comes from a rodent receptor deletion model and has not been replicated in human outcome studies.
Why the apparent ease with which male partners lose weight relates to differences in body size and maintenance calorie intake rather than a sex-specific metabolic response to a calorie deficit.
Key insight:
The hormone-based fitness claims most frequently directed at women tend to draw on mechanistic or animal data, while the long-term outcome studies — which address the actual goals of interest — show no meaningful sex difference in training response.
Topics: cycle syncing, zone two training, female fitness trends, fibre type, mitochondria, cortisol and exercise, Cushing's syndrome, fasted training, kisspeptin, rep ranges, menopause and strength training, estrogen and muscle, mechanical tension, training volume, calorie deficit, evidence-based training
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