Is there heterogeneity in muscle building among the elderly? If so, what are the detreminants of muscle building under the suggested regimen of resistance and exercise with protein intake?

The short version: yes, there is real heterogeneity, and the evidence points to baseline frailty, training dose, and protein timing as the main determinants, not age itself.

The strongest evidence for heterogeneity comes from a 2025 responder analysis in healthy older men [2]. After 16 weeks of heavy resistance training, strength gains varied widely: maximal voluntary contraction increased by 19.4% on average, but the standard deviation was 14.0%, meaning some men gained almost nothing while others gained over 30% [2]. Muscle fiber cross-sectional area varied even more, with a 14.2% average gain and a 24.9% standard deviation [2]. That is not a uniform response.

Baseline function matters. A 2025 meta-analysis of 24 trials in older adults with diagnosed sarcopenia found that resistance training improved handgrip strength by about 2.3 kg and gait speed by 0.08 m/s, but the effects on muscle mass itself were not significant [3]. The same meta-analysis identified a dose-response relationship: the minimum effective dose for handgrip strength was about 490 MET-minutes per week, with peak benefit around 1220 MET-minutes per week [3]. Below that threshold, some people got no benefit at all.

Adherence and protein intake also drive the variation. A 2025 trial in pre-frail older women found that resistance training with optimized protein intake (about 1.2 g/kg/day) reversed frailty and increased muscle protein synthesis, but adding extra leucine did nothing extra [6]. A 2017 trial in healthy older men showed that a whey-protein based supplement combined with resistance training produced greater upper-body strength gains than training alone, but the supplement alone without exercise produced only modest lean mass gains of about 1.2 kg over 6 weeks [4]. The exercise was the essential partner.

Comorbidities matter too. A 2025 study comparing young and older adults after 6 weeks of blood-flow restriction training found that older adults improved functional performance and strength but showed no significant gain in lean body mass, while young adults gained both [5]. The older adults' lower limb lean mass increased by only 0.3 kg (not significant) versus 0.4 kg in young adults (significant) [5]. Age itself is a determinant, but so is the specific training modality.

My call: The heterogeneity is real and substantial. The main determinants are baseline frailty status, training dose (below a threshold many older adults do not reach), and adequate total protein intake. Age alone is less important than these modifiable factors. Confidence: moderate – the evidence on heterogeneity is consistent across multiple trials, but the number of studies directly comparing determinants is small.