4 loss in obese, older adults relate to the documented declines in dynamic force production capability during aging, which are most notable in weight-bearing lower limb muscle groups [36, 44]. Caloric restriction is generally required to achieve signiﬁcant weight loss; typically 1/3rd to 1/4th of the lost weight is fat-free mass, a signiﬁcant concern for older adults. In contrast, exercise can preserve muscle mass [45, 46] and improve muscle quality [47, 48] in older adults, but does not typically produce signiﬁcant weight loss by itself [49]. As such, identifying interventions designed to maximize functional improvement while limiting muscle mass loss during weight loss is a current challenge. Weight loss through diet and exercise interventions may improve mobility through several mechanisms (see Figure 3). First, weight loss through caloric restriction could lessen the mechanical load on weak joints and muscles, thereby improving mobility. For example, Messier et al. found a direct association between weight loss and attenuation of knee joint moments and forces during walking in overweight and obese older adults with knee osteoarthritis following an 18-month, weight-loss intervention [21]. Speciﬁcally, this study found that each pound of weight lost was associated with a four times reduction in the load exerted on the knee per step, which would equate to more than 4,800 pounds less in compressive load per mile walked. Messier et al. [50] also looked at a subset of these participants dividing them into high, low, and no weight loss groups (groups lost 10.2%, 2.7%, and 0%, resp.). This study provided evidence that large weight loss in overweight and obese older adults reduces maximum knee compressive forces signif- icantly more than small weight losses. Collectively, these results suggest that weight loss achieved through lifestyle changes can induce biomechanical improvements in knee joints loads during walking, thereby reducing or limiting mobility impairments. Below, we review the eﬀects of lifestyle interventions involving both dietary and exercise modiﬁcation on changes in mobility function in obese, older adults. 4.1. Calorie Restriction. Negative energy balance can be achieved by reducing energy intake or increasing energy expenditure. Calorie restriction (CR) has consistently been shown to extend lifespan and reduce age-related diseases in numerous species [51]. Emerging ﬁndings also suggest that CR can produce health beneﬁts for nonobese humans (BMI range = 23.5–29.9), such as reductions in body weight and whole body fat mass [52] and beneﬁcial eﬀects on “biomarkers of aging” (i.e., fasting insulin level, core body temperature) in overweight individuals (BMI range = 25.0– 29.9) [53]. The eﬀects of CR on changes in mobility function in obese, older adults, however, are less well known. Two recent studies described below discuss the eﬀect that diet- alone interventions may have on mobility and physical function in obese, older adults. A recent study conducted by Avila and colleagues evalu- ated the eﬀect of a 10-week dietary intervention compared to a diet plus resistance training (RT) intervention on physical Journal of Aging Research Caloric restriction Caloric restriction + exercise Exercise Weight loss Strength aerobic capacity Gait speed Figure 3: Model illustrating the potential eﬀects that single- and multicomponent interventions have on gait speed. functioning in obese, older adults [54]. Both groups signiﬁ- cantly increased walking speed, documented by reduced time to complete the 400-meter walk test (reduction in time for diet: −36 sec; diet plus RT: −40 sec). These results suggest that diet alone may improve global mobility function in obese, older adults; however, these eﬀects may be heightened when a dietary and exercise intervention are combined. In an even more recent study, Villareal and colleagues conducted a clinical trial evaluating changes in physical function in obese, older adults who were randomized into a weight management program, exercise training program, weight management plus exercise training program, or con- trol group [55]. The diet-only weight management program consisted of a balanced diet producing an energy deﬁcit of 500 to 750 kcal per day from participants’ daily energy requirements. The primary measure of physical performance was the modiﬁed Physical Performance Test which included several standardized tasks such as walking 50 feet, standing up from a chair, lifting a book, and climbing one ﬂight of stairs. Compared to the control group, the diet-only weight management group signiﬁcantly improved their score on the Physical Performance Test, increased peak oxygen consump- tion, lost more fat mass, and reduced the time needed to complete an obstacle course. It is important to note, however, that, while the weight management program improved physical function in obese, older adults, the combination of diet and exercise resulted in the greatest improvements in physical function. These results are discussed further below. 4.2. Exercise Training. Epidemiological data have clearly demonstrated a dose-response pattern for physical activity to reduce the risk of mobility limitations [56, 57]. Additionally, many small clinical trials have reported beneﬁcial eﬀects of aerobic exercise on physical capacity and gait speed [58, 59]. For example, Brown and Holloszy conducted a series of studies that clearly demonstrate that aerobic exercise alone is eﬀective at increasing walking velocity through improvements from cardiovascular capacity in healthy lean, older adults [60]. Despite this knowledge, there has been little carryover to speciﬁc studies on obese, older adults. The studies discussed below provide information regarding general mobility adaptations to resistance and/or aerobic interventions in obese and nonobese older adults. Resistance exercise is the best method of improving skele- tal muscle performance. Accumulating evidence suggests