Development of Subject-Specific Proximal Femur Finite Element Models Of Older Adults with Obesity to Evaluate the Effects of Weight Loss on Bone Strength

Study background

Recommendation of intentional weight loss in older adults remains controversial, due in part to the loss of bone mineral density (BMD) known to accompany weight loss. While finite element (FE) models have been used to assess bone strength, these methods have not been used to study the effects of weight loss. The purpose of this study is to develop subject-specific FE models of the proximal femur and study the effect of intentional weight loss on bone strength.

Methods

Computed tomography (CT) scans of the proximal femur of 25 overweight and obese (mean BMI=29.7 ± 4.0 kg/m²), older adults (mean age=65.6 ± 4.1 years) undergoing an 18-month intentional weight loss intervention were obtained at baseline and post-intervention. Measures of volumetric BMD (vBMD) and variable cortical thickness were derived from each subject CT scan and directly mapped to baseline and post-intervention models. Subject-specific FE models were developed using morphing techniques. Bone strength was estimated through simulation of a single-limb stance and sideways fall configuration.

Results

After weight loss intervention, there were significant decreases from baseline to 18 months in vBMD (total hip: -0.024 ± 0.013 g/cm³; femoral neck: -0.012 ± 0.014 g/cm³), cortical thickness (total hip: -0.044 ± 0.032 mm; femoral neck: -0.026 ± 0.039 mm), and estimated strength (stance: -0.15 ± 0.12 kN; fall: -0.04 ± 0.06 kN). Adjusting for baseline bone measures, body mass, and gender, correlations were found between weight change and change in total hip and femoral neck cortical thickness (all p<0.05). For every 1 kilogram of body mass lost cortical thickness in the total hip and femoral neck decreased by 0.003 mm and 0.004 mm, respectively. No significant correlations were present for the vBMD or strength data.

Conclusion

The developed subject-specific FE models could be used to better understand the effects of intentional weight loss on bone health.

Obesity, intentional weight loss and physical disability in older adults

We examine obesity, intentional weight loss and physical disability in older adults. Based on prospective epidemiological studies, body mass index exhibits a curvilinear relationship with physical disability; there appears to be some protective effect associated with older adults being overweight. Whereas the greatest risk for physical disability occurs in older adults who are ≥class II obesity, the effects of obesity on physical disability appears to be moderated by both sex and race. Obesity at age 30 years constitutes a greater risk for disability later in life than when obesity develops at age 50 years or later; however, physical activity may buffer the adverse effects obesity has on late life physical disability. Data from a limited number of randomized clinical trials reinforce the important role that physical activity plays in weight loss programmes for older adults. Furthermore, short-term studies have found that resistance training may be particularly beneficial in these programmes as this mode of exercise attenuates the loss of fat-free mass during caloric restriction. Multi-year randomized clinical trials are needed to examine whether weight loss can alter the course of physical disablement in aging and to determine the long-term feasibility and effects of combining resistance exercise with weight loss in older adults.

Memory enhancement training for older adults with mild cognitive impairment: a preliminary study

'Mild cognitive impairment' (MCI) in older adults refers to a significant decline in memory function but not other cognitive functions. Pharmacological and non-pharmacological treatments for MCI are needed. The present randomized clinical trial tests the efficacy of a cognitive and behavioral treatment to improve memory performance and participants' attitudes about their memory. A multi-faceted intervention that included education about memory loss, relaxation training, memory skills training, and cognitive restructuring for memory-related beliefs was compared to a no-treatment control condition. Outcomes included memory performance and appraisals of memory function and control. Results indicate that the treated group had significantly better memory appraisals than controls at the end of treatment and at a six-month follow-up. There were no differences between groups on memory performance at post-test but at follow-up the trained individuals showed a trend toward better word list recall than controls. Findings suggest that individuals with MCI can benefit from multi-component memory enhancement training. Further development of such training programs and tests of their efficacy alone and in combination with medications are needed.

The effect of age on the attentional demands of postural control

A dual-task paradigm was used to determine the attentional demands of several postural control tasks in 16 older women (age, 71.5+/-3.4 years) and 14 young women (age, 25.5+/-2.4 years). Older women had slower verbal reaction times (VRT) compared with the younger women and increased reaction time more from a sitting to standing posture. Compared with the younger women, older women required more cognitive resources to maintain a simple eyes open standing posture versus an eyes open seated posture. Further, older women had significantly greater VRT during the dual-task conditions compared with younger women. However, VRT did not significantly change as the difficulty of the primary task increased in either group. These data have implications for older adults who may be at risk for falls in situations where they may be engaged in concurrent tasks, even when those tasks are considered automated and/or lower order operations.

Effect of cadence, cycling experience, and aerobic power on delta efficiency during cycling

PURPOSE

To examine the influence of cadence, cycling experience, and aerobic power on delta efficiency during cycling and to determine the significance of delta efficiency as a factor underlying the selection of preferred cadence.

METHODS

Delta efficiency (DE) was determined for 11 trained experienced cyclists (C), 10 trained runners (R), and 10 less-trained noncyclists (LT) at 50, 65, 80, 95, and 110 rpm. Preferred cadence (PC) was determined at 100, 150, and 200 W for C and R and at 75, 100, and 150 W for LT. Gas exchange at each power output (PO) was measured on a separate day, and the five cadences were randomly ordered on each occasion. It was hypothesized that: a) cyclists are most efficient at the higher cadences at which they are accustomed to training and racing, i.e., there will be a trend for DE to increase with increases in cadence; b) cyclists and runners will exhibit similar DE across the range of cadences tested; and c) DE of less-trained subjects will be lower than that of cyclists and runners.

RESULTS

PCs of C and R were similar and did not change appreciably with PO (100 W:C, 95.6 +/- 10.8; R, 92.0 +/- 8.5: 150 W:C, 94.4 +/- 10.3; R, 92.9 +/- 7.8: 200 W:C, 92.2 +/- 7.2; R, 91.8 +/- 7.9 rpm). The PC of LT was significantly lower and decreased with increases in power output (75 W: 80.0 +/- 15.3; 100 W; 77.5 +/- 15.1; 150 W; 69.1 +/- 11.9 rpm). The first hypothesis was rejected because analysis of the cyclists' data alone revealed no systematic increase in DE as cadence was increased [F(4,40) = 0.272, P = 0.894]. Repeated measures ANOVA on all three groups revealed no group x cadence interaction [F(8,112) = 0.589, P = 0.785]. Again there was no systematic effect of cadence on DE [F(4,112) = 1.058, P = 0.381]. The second and third hypotheses were also rejected since there was no group main effect, i.e., DE of cyclists, runners, and less-trained subjects were not significantly different [F(2,28) = 1.397, P = 0.264].

CONCLUSION

Pedaling cadence did not have a dramatic effect on DE in any group. Muscular efficiency, as measured indirectly by delta efficiency, appears to remain relatively constant at approximately 24%, regardless of cycling experience or fitness level.

Is a joint moment-based cost function associated with preferred cycling cadence?

Eight experienced male cyclists (C), eight well-trained male runners (R), and eight less-trained male noncyclists (LT) were tested under multiple cadence and power output conditions to determine: (1) if the cadence at which lower extremity net joint moments are minimized (cost function cadence) was associated with preferred pedaling cadence (PC), (2) if the cost function cadence increased with increases in power output, and (3) if the association is generalizable across groups differing in cycling experience and aerobic power. Net joint moments at the hip, knee, and ankle were computed from video records and pedal reaction force data using 2-D inverse dynamics. The sum of the average absolute hip, knee, and ankle joint moments defined a cost function at each power output and cadence and provided the basis for prediction of the cadence which minimized net joint moments for each subject at each power output. The cost function cadence was not statistically different from the PC at each power output in all groups. As power output increased, however, the cost function cadence increased for all three subject groups (86 rpm at 100 W, 93 rpm at 150 W, 98 rpm at 200 W, and 96 rpm at 250 W). PC showed little change (R) or a modest decline (C, LT) with increasing power output. Based upon the similarity in the mean data but different trends in the cost function cadence and PC in response to changes in power output as well as the lack of significant correlations between these two variables, it was concluded that minimiking net joint moments is a factor modestly associated with preferred cadence selection.

Perceived exertion and the preferred cycling cadence

PURPOSE

To determine whether an association exists between peripheral comfort level, as reflected by differentiated RPE measures, and the preferred cadences of subjects who differed in cycling experience and fitness level.

METHODS

Twelve experienced cyclists (C), ten runners (R), and ten less-trained noncyclists (LT), all of whom were male, pedaled at three power outputs (C, R: 100, 150, 200 W; LT: 75, 100, 150 W) and six cadences (50, 65, 80, 95, 110 rpm, and their freely chosen cadence) for 5 min per condition. Differentiated ratings of perceived exertion (RPE) were recorded during the fifth minute of the exercise. It was hypothesized that the preferred cadence selected by C, R, and LT would be the same as the cadence at which the peripheral RPE was minimized. Comparison of means failed to support this hypothesis.

RESULTS

Irrespective of rating scale (peripheral, central, overall), the cadences at which RPE was minimized were lower than the preferred cadences, except for LT at 150 W, where there was no significant difference between the preferred cadence and the cadences at which the peripheral and overall RPE were minimized. C tended toward a more curvilinear RPE-cadence relationship compared with R and LT. Mean data for all groups showed that only the peripheral RPE decreased from 50 to 65 rpm, whereas peripheral, overall, and central RPE remained essentially unchanged from 65 to 80 rpm but increased from 80 to 110 rpm. There was a trend for the cadences at which RPE was minimized for C to be higher than the cadences that minimized RPE in either R or LT. For all groups, the cadences at which peripheral RPE was minimized were significantly higher than the cadences at which either the overall or central ratings were minimized.

CONCLUSION

The small magnitudes of change in the RPE score across cadence, particularly in C and R, suggest that RPE may not be a critical variable in cadence selection during submaximal power output cycling.

Effect of cycling experience, aerobic power, and power output on preferred and most economical cycling cadences

To determine the effects of cycling experience, fitness level, and power output on preferred and most economical cycling cadences: 1) the preferred cadence (PC) of 12 male cyclists, 10 male runners, and 10 less-trained male noncyclists was determined at 75, 100, 150, 200, and 250 W for cyclists and runners and 75, 100, 125, 150, and 175 W for the less-trained group; and 2) steady-state aerobic demand was determined at six cadences (50, 65, 80, 95, 110 rpm and PC) at 100, 150, and 200 W for cyclists and runners and 75, 100, and 150 W for less-trained subjects. Cyclists and runners (VO2max: 70.7 +/- 4.1 and 72.5 +/- 2.2 mL.kg-1.min-1, respectively) maintained PC between 90 and 100 rpm at all power outputs and both groups selected similar cadences at each power output. In contrast, the less-trained group (VO2max = 44.2 +/- 2.8 mL.kg-1.min-1) selected lower cadences at all common power outputs and reduced cadence from approximately 80 rpm at 75 W to 65 rpm at 175 W. The preferred cadences of all groups were significantly higher than their respective most economical cadences at all power outputs. Changes in power output had little effect on the most economical cadence, which was between 53.3 and 59.9 rpm, in all groups. It was concluded that cycling experience and minimization of aerobic demand are not critical determinants of PC in well-trained individuals. It was speculated that less-trained noncyclists, who cycled at a higher percentage of VO2max, may have selected lower PC to reduce aerobic demand.

The relationship between cadence and lower extremity EMG in cyclists and noncyclists

Male cyclists (N = 8) and noncyclists (N = 8) pedaled under six randomly ordered cadences (50, 65, 80, 95, 110 rpm and the preferred cadence) at 200 W to test the hypothesis that electromyographic activity of selected lower limb muscles is minimized at the preferred cadence. Average preferred cadences for cyclists (85.2 +/- 9.2 rpm) and noncyclists (91.6 +/- 10.5 rpm) were not statistically different. Only gastrocnemius EMG was affected substantially and systematically by cadence changes, increasing linearly with cadence increases. Rectus femoris and vastus lateralis EMG displayed significant quadratic and linear relationships with cadence, respectively, but EMG differences between cadences were small for both muscles. Noncyclists did not exhibit significantly different patterns of muscle activity from cyclists, although there was a trend for soleus and gastrocnemius EMG to be higher in noncyclists. The results did not support our hypothesis that lower extremity muscle activation is minimized at an individual's preferred pedaling cadence. Thus, preferred cadence selection does not appear to be related to minimization of muscle activation. Given the nonlinear relationships between muscle mechanical properties, force, and EMG it is unlikely that a simple relationship exists between EMG and muscle stress.

The association between cycling experience and preferred and most economical cadences

The purpose of this study was to compare 1) the preferred cadences and 2) the aerobic demand response to cadence manipulation of highly fit, experienced cyclists and equally fit noncyclists. Eight cyclists (C) and eight non-cyclists (NC) pedaled at 200 W under six randomly ordered cadence conditions (50, 65, 80, 95, 110 rpm and preferred cadence) on a Velodyne trainer. The VO2 responses of C and NC to cadence manipulation were similar. Both groups displayed lower VO2 values at lower cadences. VO2 differences between C and NC across cadences were not significant. Mean preferred pedaling cadence surprisingly was somewhat higher for NC (91.6 +/- 10.5 rpm) than C (85.2 +/- 9.2 rpm), but the difference was not significant. The most economical cadence was significantly lower for C (56.1 +/- 6.9 rpm) than NC (62.9 +/- 4.7 rpm). Thus, cycling experience did not substantially influence preferred cadence nor economy during moderate intensity cycling by highly fit athletes. We speculate that preferred cadence and economy similarities between C and NC are associated with similarities in the dynamic muscular training of the groups.

Step length and frequency effects on ground reaction forces during walking

It is well established that the speed of walking or running significantly affects ground reaction force (GRF) characteristics. While it is sometimes assumed that the variations in step length (SL) and step frequency (SF) also affect GRF patterns, little documentation of this can be found in the literature. Ten young adults performed overground walking at 1.43 m s-1 across a force platform under five SL conditions: preferred SL and SLs that were longer and shorter than the preferred by 5 and 10% of greater trochanter height. The contact time, anteroposterior braking and propulsive force and impulse descriptors, and vertical impulse per step increased systematically as SL increased. In contrast, vertical peak forces and impulse per meter walked showed little change with SL manipulation. Despite the systematic effect of SL on several GRF descriptors, constraint of SL and SF in gait assessments is not recommended as this would prohibit the evaluation of representative gait kinematics and kinetics. Rather, these results suggest that researchers should report SL and SF data when comparing GRF characteristics between experimental groups or conditions, and should be alert to the association between SL/SF and GRF's when interpreting GRF trends.