Manual material handling (MMH) is associated with the development of work-related musculoskeletal disorders (MSDs). Older and obese workers are more susceptible to MSDs in comparison to younger, non-obese workers. One-handed carrying is a particularly challenging form of MMH as it increases physical responses (e.g., physiological, biomechanical) compared to other methods of load carrying. While older and obese individuals are rapidly growing segments of the working population, the effects of one-handed carrying on physical responses among these populations have not been adequately studied. This dissertation examines the effects of age and obesity on the physiological, psychophysical, and biomechanical responses during one-handed carrying of various loads. First, a systematic review of the literature was performed that synthesizes the scientific literature regarding one-handed carrying as it may pertain to older and obese individuals to identify research gaps. Then, a series of experiments were conducted to evaluate the effects of one-handed carrying on the physiological, psychophysical, and biomechanical responses of older and obese people. Results of the experiments suggested that the changes in physiological and biomechanical responses were mainly attributed to the load magnitude, not age, nor obesity. Physiological responses as well as moments about the L4/L5 vertebral segments were greater among obese participants than among non-obese participants. However, the differences were mitigated when load was normalized to body weight (BW), and BW and height (BW*Ht), respectively. Additionally, older participants self-selected smaller loads to carry, on average, than those selected by younger participants. The results of this dissertation suggest that carrying small load magnitudes (less than or equal to approximately 10 kg) leads to similar responses among older and obese working-age people when compared to younger, healthy working-age people. Future research opportunities are highlighted and discussed in the context of the findings.