Edward M. Phillips

Aging, muscle activity, and balance control : physiologic changes associated with balance impairment.

Older adults demonstrate increased amounts of postural sway, which may ultimately lead to falls. The mechanisms contributing to age-related increases in postural sway and falls in the elderly remain unclear. In an effort to understand age-related changes in posture control, we assessed foot center-of-pressure (COP) displacements and electromyographic data from the tibialis anterior, soleus, vastus lateralis, and biceps femoris collected simultaneously during quiet-standing trials from elderly fallers, elderly non-fallers, and healthy young subjects. Both traditional measures of COP displacements and stabilogram-diffusion analysis were used to characterize the postural sway of each group. Regression analyses were used to assess the relationship between the COP measures and muscle activity. Elderly fallers demonstrated significantly greater amounts of sway in the anteroposterior (AP) direction and greater muscle activity during quiet standing compared with the young subjects, while elderly non-fallers demonstrated significantly greater muscle activation and co-activation compared with the young subjects. No significant differences were found between elderly fallers and elderly non-fallers in measures of postural sway or muscle activity. However, greater postural sway in both the AP and mediolateral (ML) directions and trends of greater muscle activity were found in those older adults who demonstrated lower scores on clinical measures of balance. In addition, short-term postural sway was found to be significantly correlated with muscle activity in each of these groups. This work suggests that high levels of muscle activity are a characteristic of age-related declines in postural stability and that such activity is correlated with short-term postural sway. It is unclear whether increases in muscle activity preclude greater postural instability or if increased muscle activity is a compensatory response to increases in postural sway.

High-Intensity Resistance Training Improves Muscle Strength, Self-Reported Function, and Disability in Long-Term Stroke Survivors

Background and Purpose— To evaluate the efficacy of supervised high-intensity progressive resistance training (PRT) on lower extremity strength, function, and disability in older, long-term stroke survivors. Methods— Forty-two volunteers aged 50 years and above, 6 months to 6 years after a single mild to moderate stroke, were randomized into either a control group of upper extremity stretching or a PRT group that received a 12-week supervised high-intensity resistance training program consisting of bilateral leg press (LP), unilateral paretic and nonparetic knee extension (KE), ankle dorsiflexion (DF), and plantarflexion (PF) exercises. Functional performance was assessed using the 6-minute walk, stair-climb time, repeated chair-rise time, and habitual and maximal gait velocities. Self-reported changes in function and disability were evaluated using the Late Life Function and Disability Instrument (LLFDI). Results— Single-repetition maximum strength significantly improved in the PRT group for LP (16.2%), paretic KE (31.4%), and nonparetic KE (38.2%) with no change in the control group. Paretic ankle DF (66.7% versus −24.0%), paretic ankle PF (35.5% versus −20.3%), and nonparetic ankle PF (14.7% versus −13.8%) significantly improved in the PRT group compared with the control. The PRT group showed significant improvement in self-reported function and disability with no change in the control. There was no significant difference between groups for any performance-based measure of function. Conclusions— High-intensity PRT improves both paretic and nonparetic lower extremity strength after stroke, and results in reductions in functional limitations and disability.

Muscle fiber size and function in elderly humans: a longitudinal study

Cross-sectional studies are likely to underestimate age-related changes in skeletal muscle strength and mass. The purpose of this longitudinal study was to assess whole muscle and single muscle fiber alterations in the same cohort of 12 older (mean age: start of study 71.1+/-5.4 yr and end of study 80+/-5.3 yr) volunteers (5 men) evaluated 8.9 yr apart. No significant changes were noted at follow-up in body weight, body mass index, and physical activity. Muscle strength, evaluated using isokinetic dynamometry, and whole muscle specific force of the knee extensors were significantly lower at follow-up. This was accompanied by a significant reduction (5.7%) in cross-sectional area of the total anterior muscle compartment of the thigh as evaluated by computed tomography. Muscle histochemistry showed no significant changes in fiber type distribution or fiber area. Experiments with chemically skinned single muscle fibers (n=411) demonstrated no change in type I fiber size but an increase in IIA fiber diameter. A trend toward an increase in maximal force in both fiber types was observed. Maximum unloaded shortening velocity did not change. In conclusion, single muscle fiber contractile function may be preserved in older humans in the presence of significant alterations at the whole muscle level. This suggests that surviving fibers compensate to partially correct muscle size deficits in an attempt to maintain optimal force-generating capacity.

Auricular fibrillation without other evidence of heart disease: A cause of reversible heart failure☆

I T is now well known that auricular fibrillation may occur in people without other evidence of organic heart disease. This is particularly true of the paroxysmal form of the irregularity for transient spells are frequently seen in individuals who are otherwise well. Even persistent auricular fibrillation lasting for months or years without any other evidence of organic disease, subjective or objective, has been observed occasionally. What has not been sufficiently appreciated is that such patients occasionally develop outspoken congestive heart failure and that all evidence of heart disease may disappear with complete return to a normal state if the gross irregularity can be restored to normal rhythm. In this sense there is a small but definite group of patients with moderate to advanced heart failure in whom the entire process is reversible under appropriate therapy. Finally, there is a strong suspicion, from the experience to be discussed, that some patients with irreversible congestive heart failure and auricular fibrillation started with an essentially normal heart but because of prolonged auricular fibrillation developed cardiac enlargement and heart failure. Such patients then may partially respond to digitalis and diuretics. They may develop hypertension or other cardiac complications and succumb, as most patients with organic heart disease do; this is often called chronic myocarditis with auricular fibrillation or instances of nonBoston, Massachusetts

Lower Extremity Muscle Mass Predicts Functional Performance in Mobility-Limited Elders

Objectives: This study examined the influence of lower extremity body composition and muscle strength on the severity of mobility-disability in community-dwelling older adults.Methods: Fifty-seven older males and females (age 74.2 ± 7 yrs; BMI 28.9 ± 6 kg/m2) underwent an objective assessment of lower extremity functional performance, the Short Physical Performance Battery test (SPPB). Participants were subsequently classified as having moderate (SPPB score > 7: n = 38) or severe mobility impairments (SPPB score ≤ 7: n = 19). Body composition was assessed using dual-energy X-ray absorptiometry and provided measures of bone mineral density (BMD), total leg lean mass (TLM) and total body fat. Maximal hip extensor muscle strength was estimated using the bilateral leg press exercise. Multiple logistic regression analysis was utilized to identify the significant independent variables that predicted the level of mobility-disability.Results: TLM was a strong independent predictor of the level of functional impairment, after accounting for chronic medical conditions, BMD, body fat, body weight and habitual physical activity. In a separate predictive model, reduced muscle strength was also a significant predictor of severe functional impairment. The severity of mobility-disability was not influenced by gender (p = 0.71). A strong association was elicited between TLM and muscle strength (r = 0.78, p < 0.01).Conclusions: These data suggest that lower extremity muscle mass is an important determinant of physical performance among functionally-limited elders. Such findings may have important implications for the design of suitable strategies to maintain independence in older adults with compromised physical functioning. Additional studies are warranted to assess the efficacy of lifestyle, exercise or therapeutic interventions for increasing lean body mass in this population.

Lower extremity power training in elderly subjects with mobility limitations: a randomized controlled trial

Background and aims: This study investigated whether high-velocity high-power training (POW) improved lower extremity muscle power and quality in functionally-limited elders greater than traditional slow-velocity progressive resistance training (STR). Methods: Fifty-seven community-dwelling older adults aged 74.2±7 (range 65–94 yrs), Short Physical Performance Battery score 7.7±1.4, were randomized to either POW (n=23) (12 females), STR (n=22) (13 females) or a control group of lower extremity stretching (CON) (n=12) (6 females). Training was performed three times per week for 12 weeks and subjects completed three sets of double leg press and knee extension exercises at 70% of the one repetition maximum (1RM). Outcome measures included 1RM strength and peak power (PP). Total leg lean mass was determined using dual-energy X-ray absorptiometry to estimate specific strength and specific PP. Results: During training, power output was consistently higher in POW compared to STR for knee extension (∼2.3-fold) and leg press (∼2.8-fold) exercises (p<0.01). Despite this, PP and specific PP of the knee extensors increased similarly from baseline in POW and STR compared to CON (p<0.01), and no significant time-group interaction occurred for PP of the leg extensors. However, gains in leg press specific PP were significantly greater in POW compared to both STR and CON (p<0.05). Total leg lean mass did not change within any group. Conclusions: A short-term intervention of high-velocity power training and traditional slow-velocity progressive resistance training yielded similar increases of lower extremity power in the mobility-impaired elderly. Neuromuscular adaptations to power training, rather than skeletal muscle hypertrophy, may have facilitated the improvements in muscle quality. Additional studies are warranted to test the efficacy of power training in older individuals with compromised physical functioning.

Efficacy of Whey Protein Supplementation on Resistance Exercise–Induced Changes in Lean Mass, Muscle Strength, and Physical Function in Mobility-Limited Older Adults

BACKGROUND Whey protein supplementation may augment resistance exercise-induced increases in muscle strength and mass. Further studies are required to determine whether this effect extends to mobility-limited older adults. The objectives of the study were to compare the effects of whey protein concentrate (WPC) supplementation to an isocaloric control on changes in whole-body lean mass, mid-thigh muscle cross-sectional area, muscle strength, and stair-climbing performance in older mobility-limited adults in response to 6 months of resistance training (RT). METHODS Eighty mobility-limited adults aged 70-85 years were randomized to receive WPC (40g/day) or an isocaloric control for 6 months. All participants also completed a progressive high-intensity RT intervention. Sample sizes were calculated based on the primary outcome of change in whole-body lean mass to give 80% power for a 0.05-level, two-sided test. RESULTS Lean mass increased 1.3% and 0.6% in the WPC and control groups, respectively. Muscle cross-sectional area was increased 4.6% and 2.9% in the WPC and control groups, respectively, and muscle strength increased 16%-50% in WPC and control groups. Stair-climbing performance also improved in both groups. However, there were no statistically significant differences in the change in any of these variables between groups. CONCLUSIONS These data suggest that WPC supplementation at this dose does not offer additional benefit to the effects of RT in mobility-limited older adults.

Current status of an antireflux procedure in laparoscopic Heller myotomy

Background: Persistent dysphagia and postoperative gastroesophageal reflux (GER) are the most cited reasons for surgical failure of laparoscopic Heller myotomy. Adding an antireflux procedure to Heller myotomy has been proposed to prevent reflux. We hypothesized that an antireflux procedure added to laparoscopic Heller myotomy has little effect on preventing the symptoms or long-term sequelae of GER in achalasia patients. Methods: We performed a meta-analysis of studies on human subjects reported in the English language literature from 1991 to 2001 years. Results: An antireflux procedure accompanied laparoscopic myotomy in 15 studies with 532 patients. In 6 studies of 69 patients, no antireflux procedure was added to laparoscopic myotomy. Follow-up was available on 489 patients (92%) with partial fundoplication. The rate of GER diagnosed in pH studies was 7.9% (18 of 228 patients studied), whereas only 5.9% of patients experienced symptoms of GER (29 of 489 patients followed). Of the 69 patients without fundoplication, 47 (68%) were available for follow-up. Forty patients (85%) were studied with pH monitoring postoperatively, with 4 (10%) demonstrating reflux. Six (13%) of 47 patients had symptoms of GER. The difference in the rate of GER diagnosed in postmyotomy pH studies in wrapped and nonwrapped patients was not significant (7.9 vs 10%, respectively; p = 0.75). There was also no significant difference in the incidence of postmyotomy GER symptoms in wrapped and nonwrapped patients (5.9 vs 13% respectively; p = 0.12). Conclusions: Reflux is not necessarily eliminated with the addition of a partial fundoplication. Based on the published data, recommendations cannot be made regarding the efficacy of adding an antireflux procedure to laparoscopic Heller myotomy. Prospective randomized study is needed to clarify the role of an antireflux procedure after laparoscopic Heller myotomy.

Impaired Voluntary Neuromuscular Activation Limits Muscle Power in Mobility-Limited Older Adults

BACKGROUND Age-related alterations of neuromuscular activation may contribute to deficits in muscle power and mobility function. This study assesses whether impaired activation of the agonist quadriceps and antagonist hamstrings, including amplitude- and velocity-dependent characteristics of activation, may explain differences in leg extension torque and power between healthy middle-aged, healthy older, and mobility-limited older adults. METHODS Torque, power, and electromyography were recorded during maximal voluntary leg extension trials across a range of velocities on an isokinetic dynamometer. RESULTS Neuromuscular activation was similar between middle-aged and older healthy groups, with differences in torque and power explained predominantly by muscle size. However, the older mobility-limited group demonstrated marked impairment of torque, power, and agonist muscle activation, with the greatest deficits occurring at the fastest movement velocities. Agonist muscle activation was found to be strongly associated with torque output. CONCLUSIONS Similar neuromuscular activation between the middle-aged and older healthy groups indicates that impaired voluntary activation is not an obligatory consequence of aging. However, the finding that the mobility-limited group exhibited impaired activation of the agonist quadriceps and concomitant deficits in torque and power output suggests that neuromuscular activation deficits may contribute to compromised mobility function in older adults.

Assessment of lower extremity muscle power in functionally-limited elders

Background and aims: The purpose of this study was to assess the reliability and concurrent validity of a new methodology to evaluate lower extremity muscle power in older, functionally limited men and women. Methods: A cross sectional evaluation was performed on 58 older men (n=27) and women (n=31) (74.2±0.9 years). Knee and hip (leg press) and knee extensor power were evaluated on pneumatic and isokinetic resistance equipment. Incremental single attempt power (IP) testing utilized a s ingle attempt at attaining maximum power at each of six external resistances and was compared to multiple attempt pneumatic power (MP) testing determined by the highest of 5 attempts at achieving maximum power at two set resistances and also with power determined by isokinetic dynamometry. Results: Leg press extension MP yielded significantly greater power than IP at both low (mean=225.3±11.85 and 183.9±11.52 watts respectively, p<0.001) and high (mean=249.7±15.25 and 201.7±13.18 watts respectively, p<0.001) external resistances. Knee extension MP also produced significantly greater power when compared to IP at low (mean=82.4±4.45 and 69.7±4.28 watts respectively, p<0.001) and high (mean=93.7±6.3 and 83.2±5.93 watts respectively, p<0.001) external resistances. MP testing exhibited excellent reliability at both low (leg press extension: Intra Class Correlation (ICC)=0.93, knee extension: ICC=0.87) and high (Leg press extension: ICC=0.85, Knee Extension: ICC=0.91) external resistances. MP knee extension at 70% 1 RM also showed good agreement with average isokinetic power (R2=0.636). Conclusions: These findings support the reliability and concurrent validity of MP for the evaluation of muscle power in older individuals.