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Abstract

Aging is associated with alterations in immune cell profiles and declines in skeletal muscle function, which together contribute to increased vulnerability to disease and functional impairment. While aerobic exercise is known to improve muscle function and immune health, the effects of initiating exercise later in life, particularly in females, remain poorly understood. PURPOSE: This study examined the effects of aging and late-life aerobic training on blood cell counts and forelimb grip strength in female rats. METHODS: 20 female Fisher 344 rats were assigned into three experimental groups: Young (Y, 3 months (y, n = 6), Old (O, 21 months old, n = 7), or Old Exercise (OEx, 21 months old, n = 6). The exercise group ran on a treadmill at 60% maximal speed, 10° incline, 50 min/day, 5 days/week for 8 weeks. Forty-eight hours after the last exercise session, all animals had their forelimb muscle strength assessed by grip strength (Chatillon Force Measurement system). Each rat completed three trials per test, and the average of these trials were recorded as the final measurement. Rats were euthanized at least 48 hours after the grip strength test. Blood was collected and a complete blood count with differential was analyzed. Differences among the three groups were analyzed using one-way ANOVA with significance set at p < 0.05. RESULTS: The number of red blood cells (RBC) and nucleated RBCs was similar among the three groups (P > 0.05). Regarding the amount of white blood cells, there was a significance difference between Y vs. O groups (Y: 3.424 ± 0.991; O: 2.094 ± 0.279, OEx: 2.382 ± 0.773 :, pvs. both old groups ( Y: 23 ± 5.385; O: 49.20 ± 8.408; OEx: 58.40 ± 4.393 %, ppCONCLUSION: Aging impacts both grip strength and the immune cell profile, while aerobic exercise restores muscle strength and modulates white blood cells toward youthful levels. The reduction in circulating lymphocyte percentages in the OEx group may reflect a beneficial redistribution of lymphocytes into peripheral tissues, such as skeletal muscle, for enhanced immune surveillance and tissue remodeling in response to aerobic exercise. We suggest that this exercise-induced immune modulation may play a role in supporting muscle function and mitigating age-related strength loss.

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