This evaluation of musculoskeletal stress markers (MSMs) in the Cis-Baikal focuses on upper limb activity reconstruction among the region's middle Holocene foragers, particularly as it pertains to adaptation and cultural change. The five cemetery populations investigated represent two discrete groups separated by an 800–1,000 year hiatus: the Early Neolithic (8000–7000/6800 cal. BP) Kitoi culture and the Late Neolithic/Bronze Age (6000/5800–4000 cal. BP) Isakovo-Serovo-Glaskovo (ISG) cultural complex. Twenty-four upper limb MSMs are investigated not only to gain a better understanding of activity throughout the middle Holocene, but also to independently assess the relative distinctiveness of Kitoi and ISG adaptive regimes. Results reveal higher heterogeneity in overall activity levels among Early Neolithic populations—with Kitoi males exhibiting more pronounced upper limb MSMs than both contemporary females and ISG males—but relative constancy during the Late Neolithic/Bronze Age, regardless of sex or possible status. On the other hand, activity patterns seem to have varied more during the latter period, with the supinator being ranked high among the ISG, but not the Kitoi, and forearm flexors and extensors being ranked generally low only among ISG females. Upper limb rank patterning does not distinguish Early Neolithic males, suggesting that their higher MSM scores reflect differences in the degree (intensity and/or duration), rather than the type, of activity employed. Finally, for both Kitoi and ISG peoples, activity patterns—especially the consistently high-ranked costoclavicular ligament and deltoid and pectoralis major muscles—appear to be consistent with watercraft use. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc.