Why Women Lose Metabolic Power With Age and How to Get It Back

Sims places HIIT as one of the two pillars (alongside resistance training) to fix metabolic dysfunction. She notes that many people do moderate-intensity 'intervals' that don't produce the necessary stress. The goal is to push the body to an epigenetic shift in muscle cells that makes them less insulin-dependent, improving glucose disposal. Combined with resistance training, this retrains the hypothalamus and appetite signals. The protocol is not about burning calories during the workout but about long-term metabolic adaptation. She challenges the 'slow metabolism' excuse by asserting that the feedback mechanisms that determine metabolic rate can be rebooted through this intense stimulus.

Sims ties resistance training directly to the complaint of a slow metabolism. She explains that building muscle creates more 'metabolically active tissue', which increases your basal metabolic rate. This is fundamental and non-negotiable. She pairs it with HIIT to address metabolic feedback dysfunction. The combination ensures that the body doesn't just burn more calories at rest but also improves insulin sensitivity and appetite regulation. The advice is simple but often overlooked; many women avoid heavy weights fearing bulkiness, but Sims insists that lifting is crucial for metabolic health, not just aesthetics.

Sims' argument is a direct challenge to the 'cardio queen' phenomenon and the fear that lifting heavy makes women bulky. She asserts that the female body is wired for efficiency in long, slow activities, which becomes a liability with age. Without power training, the body defaults to being 'slow and a little bit heavier' because it's adapted to endurance. She draws from her own life: she loves long outdoor adventures but never neglects the gym. She started lifting at 15 thanks to a friend's brother and felt the benefit of power throughout her endurance career. The protocol is not optional; it's a non-negotiable for healthy aging. Even if your genes say endurance, your gym time should mimic a power athlete's.

Sims directly addresses the excuse she hears from gym-goers struggling with fat loss: 'I have a slow metabolism.' She doesn't deny metabolic individualities but argues that what people refer to as a slow metabolism often reflects a breakdown in the body's feedback loops for metabolic control — appetite signaling, hypothalamic cues that tell the body to build muscle and burn fat. By engaging in high-intensity work and resistance training, you create a strong stress that forces the body to improve insulin sensitivity (via epigenetic changes in muscle), use glycogen more efficiently, and increase lean mass. This, in turn, resets the feedback mechanisms, countering the sluggishness. She is essentially saying: your metabolic rate is not a fixed thermostat; it's a modifiable system. This is a call to action rather than resignation.

Sims addresses the host's query about women who genetically lean toward endurance sports. She admits she herself is an endurance lover who uses outdoor activity for mental escape, but she has always lifted weights since age 15, drawn by the feeling of power. For women, the physiology is clear: they have a preponderance of slow-twitch (oxidative) fibers. As they age, estrogen and progesterone perturbations cause a loss of glycolytic capacity and the nerve signaling required for strong muscle contractions. Without specific power training, the female body defaults to its natural slow, fat-storing mode — becoming not just metabolically slower but also heavier. Thus, the gym work for an endurance athlete should not differ markedly from a power athlete; every woman needs to lift heavy and train explosively to counteract this biological tendency, maintain muscle mass, and keep metabolic health. Her personal anecdote reinforces that an endurance identity doesn't negate the need for power.