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Functional independence is an important aspect of successful aging and differs with age and by sex in humans. Physical performance often declines earlier than other age-associated functional impairments. Rodent models are used to study pharmacological/toxicological effects of human therapies. However, physical outcomes in mice are usually assessed for short periods, with limited information on the influence of age and sex. Here, we investigated how age and sex affected murine physical performance over 23 hours of continuous observation. Young (3 months) and old (22 months) C57BL/6JArc male and female mice were assessed using the Laboratory Animal Behavior Observation, Registration, and Analysis System. Mice were individually housed for recording of distance travelled, mean gait speed, and durations of different physical activities. Compared to young mice of the same sex, old mice travelled significantly shorter distances with slower gait speeds and shorter durations of locomotion, rearing, climbing, and immobility. Older mice groomed significantly more than young mice. Old females reared more during the light cycle than old males. Young females climbed substantially more than young males. Significant Age * Sex interactions were detected for rearing and climbing, whereby an age-related decline was greater in males than in females. Our results suggest that old age reduces exploratory activities and increases grooming in mice. Age-related declines vary between sexes and tend to be greater in males. This noninvasive assessment can be applied to investigate how different interventions affect rodents of different ages and sexes, through the day–night cycle.

Males and females may respond differently to medications, yet knowledge about sexual dimorphisms in the effects of polypharmacy remains limited, particularly in aging. This study aimed to assess the effect of high Drug Burden Index (DBI) polypharmacy treatment compared to control on physical function and behavior in young and old, male and female mice. We studied whether age and sex play a role in physical function and behavior following polypharmacy treatment and whether they are paralleled by differences in serum drug levels. Young (2.5 months) and old (21.5 months), C57BL/6 mice were randomized to control or high DBI polypharmacy treatment (simvastatin, metoprolol, oxybutynin, oxycodone, and citalopram; n = 6–8/group) for 4–6 weeks. Compared to control, polypharmacy reduced physical function (grip strength, rotarod latency, gait speed, and total distance), middle zone distance (increased anxiety), and nesting score (reduced activities of daily living) in mice of both ages and sexes (p < .001). Old animals had a greater decline in nesting score (p < .05) and midzone distance (p < .001) than young animals. Grip strength declined more in males than females (p < .05). Drug levels at steady state were not significantly different between polypharmacy-treated animals of both ages and sexes. We observed polypharmacy-induced functional impairment in both age and sex groups, with age and sex interactions in the degree of impairment, which were not explained by serum drug levels. Studies of the pathogenesis of functional impairment from polypharmacy may improve management strategies in both sexes.

The mouse clinical frailty index and the mouse frailty phenotype assessment are two recently developed tools used to assess frailty in mice. The objectives of this study were to investigate whether the same mice are identified as frail with both tools and to examine the association of each of the assessment tools with age and frailty-related outcomes. Frailty was measured using both tools in old (~24 months; n = 36) C57BL/6 male mice. After 2 weeks, blood pressure and heart rate were measured and serum samples were collected for analysis of alanine aminotransferase, creatinine, and albumin levels. The mouse frailty phenotype assessment identified no mice as frail but modification of the assessment tool identified six mice as frail. The mouse clinical frailty index identified 16 mice as frail and the agreement between the two scales was 50.0%. Increasing clinical frailty index scores were correlated with low serum alanine aminotransferase, as well as decreased heart rate, and reduced heart rate variance. We conclude that, consistent with equivalent frailty assessment scales in humans, both tools have value but do not necessarily identify the same mice as frail.