Comparison of Body Composition Methods for Estimating Body Fat Percentage in Lower Limb Prosthesis Users.

BACKGROUND: There is a dearth of literature evaluating the accuracy of Air Displacement Plethysmography (ADP) compared to Dual-energy X-ray Absorptiometry (DXA) for assessing body composition in individuals with lower limb amputations. Validity of ADP in persons with lower limb amputations must be established. OBJECTIVE: The objective of this study was to compare body composition in persons with lower limb amputations using the BOD POD® and DXA. METHODOLOGY: Body composition was performed on eleven lower limb prosthesis users (age 53.2±14.3 years, weight 81.9±22.3kg) using ADP and DXA with and without prosthesis. FINDINGS: Repeated measures ANOVA indicated no significant difference in body composition among and between trials, F(3,8)= 3.36, p= 0.075. There were no significant differences in Body Fat (BF) percentage with and without prostheses on the BOD POD (28.5±15.7% and 33.7±12.1%, respectively) nor the DXA (32.9±10.6% and 32.0±9.9%, respectively). Association between the BOD POD and DXA were greatest when prostheses were not worn compared to when they were worn. Bland-Altman plots indicate agreement between BOD POD® and DXA was greatest while wearing the prosthesis. CONCLUSION: This study is a first to compare total body fat percent between the BOD POD® and DXA in lower limb prosthesis users. BOD POD® report valid indices of BF%. Future work will utilize the BOD POD® in intervention studies for monitoring body composition changes across the continuum of rehabilitation.

Musculoskeletal Outcomes from Chronic High-Speed, High-Impulse Resistance Exercise.

While bones and muscles adapt to mechanical loading, it appears that very specific types of stimuli must be applied to achieve osteogenesis. Our study assessed musculoskeletal outcomes to 30 training sessions on an Inertial Exercise Trainer (Newnan, GA). Subjects (n=13) performed workouts with their left leg, while their right served as an untreated control. Workouts entailed three 60-s sets each of knee extension, hip extension and calf press exercises, separated by 90-s rests. Before and after the 30 training sessions, subjects underwent strength tests (knee and ankle extensors of both legs), DEXA scans (hip, knee and ankles of both legs), and blood draws. After 30 training sessions 2×2 ANOVAs showed left leg peak torques rose significantly. 2×2 ANCOVAs, with bone scan area as a covariate, showed significant left leg calcaneal bone mineral content (+29%) and density (+33%) increases after 30 training sessions. A significant decline in C-terminal telopeptides of type I collagen, a blood marker of bone resorption, also occurred after 30 training sessions. The Inertial Exercise Trainer's large volume of training session repetitions elicited high peak force, peak acceleration and impulses that likely provided a mechanical loading stimulus that evoked calcaneal accretion.

The anabolic response to resistance exercise and a protein-rich meal is not diminished by age.

OBJECTIVES: The synergistic effect of resistance exercise and protein ingestion on muscle protein anabolism in young adults has been well described. However, it is unclear if this relationship is maintained in older adults who are at greater risk of sarcopenic muscle loss. To this end, we sought to determine if the synergistic response to a bout of resistance exercise and a protein-rich lean beef meal was altered by age. SETTING: The University of Texas Medical Branch, Clinical Research Center, Galveston, Texas. PARTICIPANTS: Healthy young (n=7, 29±3 y) and older (n=7, 67±2 y) adults. DESIGN: Mixed muscle fractional synthesis rate (FSR) was calculated during a 3 h post-absorptive/rest period and again during a 5 h period following ingestion of a protein-rich meal (340 g lean beef) and bout of resistance exercise (6 sets of 8 repetitions of isotonic knee extension exercise at 80% one repetition maximum). MEASUREMENTS: Venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed (2.0 µmol/kg) constant infusion (0.08 µmol∙kg(-1)min(-1)) of L- [ring-13C6] phenylalanine. RESULTS: Mixed muscle FSR increased by approximately 108% in both young [pre: 0.073±0.008; post: 0.156±0.021(SE) %/h, p<0.001] and older adults (pre: 0.075±0.004; post: 0.152±0.017 %/h, p=0.003) following the meal and resistance exercise bout. CONCLUSION: Aging does not diminish the increase in muscle protein synthesis following a high-quality protein rich meal and bout of resistance exercise.

Effects of muscle fiber motion on diffuse correlation spectroscopy blood flow measurements during exercise.

The influence of muscle fiber motion during exercise on diffuse correlation spectroscopy (DCS) measurements of skeletal muscle blood flow is explored. Isotonic (with muscle fiber motion) and isometric (without muscle fiber motion) plantar flexion exercises were performed at 30% of maximal force on a dynamometer, and muscle blood flow was continuously monitored on the medial gastrocnemius (calf) muscle of a healthy volunteer using DCS. During exercise, dynamometer recordings including footplate position, footplate angular velocity, and plantar flexion torque were obtained. Muscle fiber motions introduced artifacts into the DCS signals, causing an overestimation of blood flow changes. We show how proper co-registration of dynamometer recordings and DCS measurements enables separation of the true blood flow responses during exercise from those affected by the motion artifacts.

Artificial gravity maintains skeletal muscle protein synthesis during 21 days of simulated microgravity.

We sought to determine the effects of longitudinal loading (artificial gravity) on skeletal muscle protein kinetics in 15 healthy young males after 21 days of 6 degrees head-down tilt bed rest [experimental treatment (Exp) group: n = 8, 31 +/- 1 yr; control (Con) group; n = 7, 28 +/- 1 yr, means +/- SE]. On days 1 and 21 of bed rest, postabsorptive venous blood samples and muscle biopsies (vastus lateralis and soleus) were obtained during a 1-h pulse bolus infusion protocol (0 min, l-[ring-(13)C(6)]phenylalanine, 35 mumol/kg; 30 min, l-[ring-(15)N]phenylalanine, 35 mumol/kg). Outcome measures included mixed muscle fractional synthesis (FSR) and breakdown rates (FBR). The Exp group experienced 1 h of longitudinal loading (2.5G at the feet) via a short-radius centrifuge during each day of bed rest. Mixed muscle FSR in the Con group was reduced by 48.5% (day 1, 0.081 +/- 0.000%/h vs. day 21, 0.042 +/- 0.000%/h; P = 0.001) in vastus lateralis after 21 days of bed rest, whereas the Exp group maintained their rate of protein synthesis. A similar but nonsignificant change in FSR was noted for the soleus muscle (Exp, -7%; Con, -22%). No changes in muscle protein breakdown were observed. In conclusion, 1 h of daily exposure to artificial gravity maintained the rate of protein synthesis of the vastus lateralis and may represent an effective adjunct countermeasure to combat the loss of muscle mass and functional during extended spaceflight.

Functional and metabolic consequences of sarcopenia.

Sarcopenia associated with the normal aging process is often combined with the detrimental effects of a sedentary lifestyle in older adults, leading to a significant reduction in reserve capacity of the neuromuscular system. A clear example of the aging effect is the pattern of reduction in muscle strength after the sixth decade for both isometric and concentric contractions. However, older adults are relatively stronger for movements in which muscles lengthen, due to the inherent advantage of eccentric contractions, plus their stiffer muscle structures and prolonged myosin cross-bridge cycles. Also, the capacity for physiological adaptations in the motor pathways remains into very old age when an appropriate exercise stimulus is given, and older adults can obtain adaptations in both enhanced neural control of motor units and increased protein synthesis leading to moderate muscle hypertrophy. Since periods of sedentary lifestyle or bed rest due to illness can have severe detraining consequences on the neuromuscular function of an older person, long-term prevention strategies are advocated to avoid excessive physical impairments and activity restrictions in this age group.