David H. Nielsen

Relationships Among Impairments in Lower-Extremity Strength and Power, Functional Limitations, and Disability in Older Adults

Background and Purpose: During the aging process, older adults may experience a loss of strength and power, which then may lead to functional limitations and disability. The purpose of this study was to examine how impairments in lower-extremity strength and power are related to functional limitations and disability in community-dwelling older adults. Subjects: Thirty older adults (age [X̄±SD], 77.3±7.0 years; 25 women and 5 men) with mild to moderate functional limitations participated in this study. Methods: Lower-extremity strength, peak power, power at a low relative intensity, and power at a high relative intensity were measured with a pneumatic resistance leg press. Functional limitations and disability were assessed with the Short Physical Performance Battery (SPPB), the Six-Minute Walk Test (SMWT), and the Late Life Function and Disability Instrument (LLFDI). Results: All measures of strength and power were related to functional limitations. Peak power demonstrated the strongest relationships with SMWT, the SPPB gait speed subscale, and the LLFDI functional limitation component. Power at a high relative intensity demonstrated the strongest relationships to the SPPB total score and the SPPB sit-to-stand subscale score. All measures of strength and power were indirectly related to the LLFDI disability component. Discussion and Conclusion: Older adults should focus on increasing and maintaining lower-extremity strength and power across a range of intensities in order to decrease functional limitations and disability.

Cross-validation of the slaughter skinfold equations for children and adolescents

Prior to sexual maturation, children and adolescents have more water and less bone mineral content than adults, resulting in less dense fat-free body mass (FFM). This suggests that previously established adult skinfold/density equations are inappropriate for use with children and adolescents for the prediction of body fatness (%BF) and FFM. To overcome this problem, Slaughter and colleagues have introduced new skinfold (SKF) equations that take into account the changing density of FFM in children and adolescents as they mature. The purpose of our study was to cross-validate a select set of the Slaughter SKF equations by comparing them with a criterion measurement (Lohmans Siri age-adjusted body density equation) in 122 subjects ranging in sexual maturation from pre- to post-pubescent and ranging in age from 8-17. Our cross-validation found very high intraclass (reliability) correlations (ICCs = 0.98-0.99) and high validity correlations (rs = 0.79-0.99). The standard errors of the estimate for %BF ranged from 3.5-4.6% and total errors for %BF ranged from 3.6-4.6%. The Slaughter equation using tricep and calf SKF for females was significantly different (P < 0.05) from the criterion measure in its prediction of %BF. In males, there was an interaction between the SKF equation and subject maturation level. The data indicate that the Slaughter SKF equations hold promise for estimating body composition in children and adolescents but are still in need of refinement.

Wrestlers' minimal weight : anthropometry, bioimpedance, and hydrostatic weighing compared

The need for accurate assessment of minimal wrestling weight among interscholastic wrestlers has been well documented. Previous research has demonstrated the validity of anthropometric methods for this purpose, but little research has examined the validity of bioelectrical impedance (BIA) measurements. Comparisons between BIA systems has received limited attention. With these two objectives, we compared the prediction of minimal weight (MW) among 57 interscholastic wrestlers using three anthropometric methods (skinfolds (SF) and two skeletal dimensions equations) and three BIA systems (Berkeley Medical Research (BMR), RJL, and Valhalla (VAL]. All methods showed high correlations (r values greater than 0.92) with hydrostatic weighting (HW) and between methods (r values greater than 0.90). The standard errors of estimate (SEE) were relatively small for all methods, especially for SF and the three BIA systems (SEE less than 0.70 kg). The total errors of prediction (E) for RJL and VAL (E = 4.4 and 3.9 kg) were significantly larger than observed nonsignificant BMR and SF values (E = 2.3 and 1.8 kg, respectively). Significant mean differences were observed between HW, RJL, VAL, and the two skeletal dimensions equations, but nonsignificant differences were observed between HW, BMR, and SF. BMR differed significantly from the RJL and VAL systems. The results suggest that RJL and VAL have potential application for this subpopulation. Prediction equation refinement with the addition of selected anthropometric measurement or moderating variables may enhance their utility. However, within the scope of our study, SF and BMR BIA appear to be the most valid methods for determining MW in interscholastic wrestlers.

the Relationship between Lower Extremity Strength and Power to Everyday Walking Behaviors in Older Adults with Functional Limitations

Purpose: While lower extremity strength and power show a relationship to laboratory measures of walking in older adults, the relationship of strength and power to walking behaviors in a community setting is unclear. The purpose of this study was to examine the relationship between lower extremity strength, peak power, power at a low relative intensity, and power at a high relative intensity to everyday walking behaviors in older adults. Methods: Thirty community‐dwelling older adults (mean age = 77.3 ± 7.0, 25 females, 5 males) took part in the study. Lower extremity strength and power were measured with a pneumatic resistance leg press. An accelerometer activity monitor was used to measure walking behaviors across 6 days with total steps, distance, and walking speed used as outcome measures. Results: Peak power (R2 = 0.16) was significantly related to total steps. Strength (R2 = 0.23), peak power (R2 = 0.44), power at low relative intensity (R2 = 0.41), and power at high relative intensity (R2 = 0.34) were significantly related to distance. Strength (R2 = 0.39), peak power (R2 = 0.50), power at low relative intensity (R2 = 0.38), and power at high relative intensity (R2 = 0.48) were significantly related to walking speed. Conclusions: Lower extremity strength, peak power, power at a low relative intensity, and power at a high relative intensity are all related to walking behaviors in older adults with peak power having the strongest relationship.

Mechanical Gait Analysis of Transfemoral Amputees: SACH Foot Versus the Flex-Foot

The purpose of this study was to identify gait mechanics that might explain the physiological benefits found when transfemoral amputees walked over ground using a Flex-Foot® compared to a SACH foot fastened below a hydraulic knee joint. Five active traumatic unilateral transfemoral amputees were videotaped as they walked overground at five controlled speeds ranging from 1.5 to 3.5 mph on a continuous path. Analysis of the videotape data was conducted on the mean step length, early and late swing and stance phases, and double- and single-support phases for each speed. Since there were no speedby- foot-type statistical interactions, the foot-type comparisons could be made across all speeds. The only significant differences due to foot type were found in the uninvolved double- and uninvolved single-support phases and the late stance-phase ratio (involved late stance phase/uninvolved late stance phase). These differences appear to be caused by a delay in the involved toe-off while using the Flex-Foot. The Flex-Foot is designed to deform during weight acceptance and reform giving a “pushoff” during late stance. The additional time needed to reform the Flex-Foot could explain the phase differences, and this pushoff mechanism could explain the physiological benefits of walking with the Flex-Foot compared to the SACH foot. With a pushoff, the inertia of the involved limb may be overcome, and the prosthetic limb may be recovered with less upper-body movement and thus less energy would be expended, resulting in a more efficient, symmetrical gait.

Systolic blood pressure responses during isometric contractions of large and small muscle groups

The purpose of this study was to test for a difference between the systolic blood pressure responses to voluntary contractions of large and small muscle groups of the upper extremity. Systolic blood pressure was measured at approximately 20 sec intervals during sustained isometric contractions of the index finger adductors and handgrip muscles contracting at 40% of maximal voluntary contraction (MVC). Contractions were terminated when EMG activity exceeded 10% of maximal activity of selected accessory muscles or when the 40% MVC tension could no longer be held constant (+/-10%). The slopes of the regression lines representing systolic blood pressure responses to sustained isometric contraction of a small and large muscle group of the upper extremity were significantly different (p less than .001). Older theories that pressor responses are determined only by the % MVC and not by the mass of contracting muscle need to be reexamined.

Effects of a maximal graded exercise test on glutathione as a marker of acute oxidative stress.

PURPOSE Strenuous exercise in animal studies has been shown to cause acute oxidative stress due to the generation of oxygen-centered free radicals reflected in lower levels of glutathione (GSH), higher levels of glutathione disulfide (GSSG), and a drop in GSH:GSSG ratios, the maintenance of which is crucial for a variety of cell functions. Human studies on this topic are limited. The purpose of this study was to investigate the effects of a maximal graded exercise test GXTmax (modified Bruce protocol) on GSH as a marker of acute oxidative stress, and whether full recovery will occur at 60 minutes postexercise. METHODS Eighty sedentary subjects were used as a sample of convenience. Venous blood samples for GSH and GSSG were collected directly before, immediately after, and 60 minutes post-GXTmax. Repeated-measures analysis of variance and Bonferroni adjusted t tests (post-GXTmax) versus resting, and 60 minutes recovery versus resting) were used for data analysis. RESULTS As an acute response to maximal exercise, the GSH levels dropped significantly from a resting baseline value of 1025.75 microM to an immediate post-GXTmax value of 893.30 microM (pooled SE = 7.17 microM). The GSSG levels significantly increased from 2.24 microM to 3.15 microM (pooled SE = 0.03 microM). The GSH:GSSG ratio levels significantly dropped from baseline 462.12 to 276.40 postexercise (pooled SE = 5.98). The blood GSH, GSSG, and GSH:GSSG ratio levels showed no significant difference at 60 minutes post-GXTmax when compared with resting values, indicating full recovery. CONCLUSION The current results indicated that in sedentary individuals, a maximal treadmill GXT is an effective technique for inducing acute oxidative stress as evidenced by GSH system responses, with full return to resting baseline levels within 60 minutes of recovery. The potential for using this model in assessing oxidative stress responses to cardiac and pulmonary rehabilitation is of clinical interest, with a need for further investigation.

Transfemoral Amputee Physiological Requirements: Comparisons Between SACH Foot Walking and Flex-Foot Walking

This study compared exercise intensity, oxygen uptake and gait efficiency when active traumatic transfemoral amputees used a SACH foot or a Flex-Foot® attached below a hydraulic knee joint. The five male subjects completed two test sessions, one with each foot, one week apart. They walked overground at five controlled speeds ranging from 1.5 mph to 3.5 mph (40.2 m/sec to 93.9 m/sec). For each condition, when subjects had reached physiological steady state, heart rate was recorded by telemetry, and expired gas was collected in a Douglas bag and analyzed in the laboratory. There was no statistical interaction between foot type and speed allowing foot-type comparisons to be made across speed. Results of the measures analysis of variance (ANOVA) were recorded. The analyses indicate Flex-Foot walking was associated with significantly lower exercise intensity, less energy expenditure and improved gait efficiency compared to the SACH foot. The results of this study indicate the Flex-Foot is physiologically beneficial for active traumatic transfemoral amputees walking overground across a functional range of walking speeds. While the differences are relatively small, they may be clinically important given the high energy cost of transfemoral amputee walking.

Criterion methods of body composition analysis for children and adolescents

The lack of chemical maturity, subsequent to normal growth and maturation, complicates the assessment of body composition in children. Even though known to overpredict percent body fat (%BF), the use of adult prediction equations is widespread in the pediatric literature. Many sex‐ and age‐specific modified equations have been proposed. This study reports a cross‐validation analysis of selected laboratory‐based criterion methods in an attempt to identify the most appropriate reference which could be used in future validation studies of the more practical field/clinical testing methods. Subjects were 48 (24 boys and 24 girls) peripubertal children evenly distributed according to stage of maturation. Criterion measurements included body density (Db) by hydrostatic weighing, total body water (TBW) by deuterium oxide dilution, and total body mineral content (TMC) by dual energy x‐ray absorptiometry. Five different prediction models were evaluated. Test‐retest reliabilty was high (ICC = .970 to .999). Of the prediction models tested, the four‐component model was considered the most accurate laboratory‐based criterion model since it involves measurement of the primary constituents of fat‐free mass. Based on high r2 (≥.942) values, low standard errors of estimate (SEE = 1.8 %BF males, 1.1 %BF females); and low total prediction errors (TE = 1.9 %BF males, 2.0 %BF females), the Lohman age‐adjusted prediction equation showed the best agreement with the four component model. If multiple testing facilities are unavailable, the Lohman two‐component (Db) model would be the criterion method of choice.

AMBULATION OF CHILDREN WITH MYELOMENINGOCELE: PARAPODIUM VERSUS PARAPODIUM WITH ORLAU SWIVEL MODIFICATION

The feasibility of ambulation for children with high spinal lesions is questionable because of the relatively high exercise intensity and energy cost required, so orthotics designed for ambulation must keep energy expenditure to a minimum. This study determined the self‐selected walking velocity and maximum walking velocity of 10 paraplegic children using two orthotic devices, the parapodium and swivel walker, and compared the energy cost, gait efficiency and relative exercise intensity (per cent maximum heart‐rate). Walking velocities were significantly higher with the parapodium, but energy cost and gait efficiency were significantly better with the swivel walker. Differences between the two devices in relative exercise intensity were not significant. Although walking velocity is slower, the lower metabolic cost appears to give the swivel walker an advantage over the parapodium.