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PubMed2006

Patterns and correlates of muscle strength loss in older women.

BACKGROUND: The aging process is associated with progressive declines in muscle strength, resulting in functional disability and reduced quality of life. OBJECTIVE: The purpose of this epidemiological study was to examine the age-related loss of grip strength both cross-sectionally and longitudinally and the risk factors associated with the decline in muscle strength in a large population of community-living older women (aged 65-91 years). METHODS: Clinical visits, including physical examinations and lifestyle assessment, were conducted at baseline and biennially afterwards for a total of 10 years of follow-up. The upper-body muscle strength was measured by grip strength using a hand-held dynamometer. RESULTS: The muscle strength decreased cross-sectionally (n = 9,372) as well as longitudinally (n = 5,214), as age increased, and the decline in muscle strength measured during follow-up was greater than that measured cross-sectionally at baseline. The average loss of grip strength during 10 years of follow-up was 5.1 kg, equivalent to a rate of 2.4% decline per year, with the greatest loss seen in the oldest age group (80 years or older). Cross-sectional analysis revealed that the correlates of lower muscle strength included older age, greater weight, greater height loss since age 25 years, lower protein intake, difficulties in functional tasks, and lower physical activity. In longitudinal analysis, older age, baseline strength, weight and height loss during follow-up, difficulties in functional tasks, and lower physical activity were found to be significantly and independently associated with greater loss in grip strength during follow-up. CONCLUSIONS: Cross-sectional and longitudinal analyses of age-related loss of muscle strength yielded different rates of decline. In addition to older age and difficulties in functional tasks, a number of modifiable factors, including weight and physical activity, are associated with increased decline in muscle strength among older women.

Age Factors↗

PubMed1992

Effect of ionic strength on the regulatory properties of 2-oxoglutarate dehydrogenase complex.

The effects of changing ionic strength on the activity of the 2-oxoglutarate dehydrogenase complex from pig kidney cortex were explored. This enzyme complex is found to be influenced in many ways by the ionic strength of the reaction medium. The enzyme shows an optimum activity at 0.1 M ionic strength. Increase in ionic strength from 0.1 M to 0.2 M resulted in a decrease of S0.5 for 2-oxoglutarate, and in an increase of S0.5 for NAD. Changes in ionic strength over the range of 0.05-0.2 M have little, if any, effect on S0.5 for CoA. The Hill coefficient for 2-oxoglutarate and NAD at 0.2 M ionic strength was 1.0, whereas at 0.05 M ionic strength it was 0.85 and 1.2 for 2-oxoglutarate and NAD, respectively. At 0.05 M ionic strength the pH optimum of the enzyme ranges between 7.4-7.6, but at 0.15 M ionic strength the pH optimum shifts to 7.8. The magnitude of inhibition of enzyme activity by ATP is not influenced by changes in ionic strength in the absence of calcium. However, in the presence of Ca2+, increases in ionic strength lower the inhibitory effects of ATP. The Si0.5 for ATP in both presence and absence of Ca2+ was not affected by changes in ionic strength in the range of 0.1-0.2 M. In contrast, the Sa0.5 for ADP in the absence of Ca2+ decreases as ionic strength increases. In the presence of calcium and 0.2 M ionic strength ADP has no effect on 2-oxoglutarate dehydrogenase complex activity.

Adenosine Diphosphate↗

PubMed1997

Comparison of bond strengths of denture base resins to nickel-chromium-beryllium removable partial denture alloy.

PURPOSE: In vitro bond strengths of a traditional denture base resin (Lucitone 199) and three adhesive denture base resins (Meta-Dent, Meta-Fast with liner, and Meta-Fast without liner) to treated nickel-chromium-beryllium (Ni-Cr-Be) partial denture alloy were tested with four alloy surface pretreatments (sandblast, Met-etch, Rocatec with silane, and Rocatec without silane), with or without primer (Dentsply). The Lucitone 199 resin bonded to the nonprimed sandblasted group was the control group. The hypothesis was the use of alloy pretreatments and/or primer does not improve the bond strength of denture base resins to sandblasted Ni-Cr-Be partial denture alloy. MATERIAL AND METHODS: Primed and nonprimed bonded specimens were prepared and finished, stored in 37 degrees C distilled water for 24 hours, then debonded in tension on a testing machine. The bond strength was calculated in megapascals (MPa). Five specimens were prepared and tested for each experimental condition, both with and without primer, for a total of 160 specimens. RESULTS: For three-way analysis of variance, the main effects of resins and treatment were statistically significant (p < 0.05), but the main effect of primer was not statistically significantly (p > 0.05). Without primer, the control group had the lowest bond strength (0 MPa). The three adhesive resin groups produced significantly higher bond strengths than the Lucitone resin groups. For the treated groups, nearly all sandblasted groups produced significantly lower bond strength than the other three treated groups. Meta-Dent to Met-etch treated group had the highest bond strength (23.9 MPa). With primer, the bond strengths of the Lucitone resin groups were significantly higher than the nonprimed groups, and the Lucitone resin-primed Rocatec treated group had the highest bond strength (14.8 MPa). For the three adhesive denture base resins, nearly all primed treated groups had significantly lower bond strengths than nonprimed groups. CONCLUSIONS: Without primer, the Lucitone resin-sandblast treated group (control) had the lowest bond strength (0 MPa). The Meta-Dent denture base resin with the Met-etch treated group had the highest bond strength (23.9 MPa). With primer, the Lucitone resin-primed Rocatec-silane treated group had the highest bond strength (14.8 MPa). For the adhesive denture base resins, nearly all bond strengths of the primed treated groups were significantly lower than the values of the nonprimed groups.

Acid Etching, Dental↗

PubMed2003

Back strength cannot be predicted accurately from anthropometric measures in subjects with and without chronic low back pain.

OBJECTIVES: (1) To develop a multiple regression equation using anthropometric measurements to predict back strength and (2) to estimate the effect of practice on the back strength results and back strength predictions. DESIGN: Comparative study with repeated measures performed on three days. BACKGROUND: The assessment of back muscle relative endurance (% maximal strength) requires the measurement of maximal back strength which is problematic with low back pain patients. METHODS: The back strength (L5/S1 static extension moment), age and 26 anthropometric parameters were obtained from 83 male volunteers [42 healthy subjects and 41 chronic low back pain patients] aged between 20 and 60 years. A subsample of 20 healthy subjects and 20 patients were assessed through three days of testing to evaluate the variations of back strength with practice. RESULTS: The final regression model (n=42 healthy subjects) explained 39% of the variance in back strength. Back strength increased with practice (Day1<Day2 & 3) for both healthy and patients groups. However, the error of prediction of back strength derived from the regression model showed a significant improvement with practice for the patients only. CONCLUSIONS: Back strength cannot be predicted from simple anthropometric measures without important errors. The decrease of the error of prediction obtained for the patient group is indicative of a decreasing influence of psychological factors that are independent of motor learning because the effect of motor learning would have occurred on both groups if present. RELEVANCE: The prediction of back strength would be useful to determine (1) the relative force level of a given exercise or (2) the preinjury back strength. Unfortunately, anthropometric measurements are not enough good predictors of back strength.

Adult↗

PubMed2003

Axial neck rotation strength in neutral and prerotated postures.

OBJECTIVE: To characterize isometric rotation strength in the neutral and in different prerotated positions of the neck. DESIGN: This was a descriptive study involving maximal isometric strength measurements of the cervical musculature. BACKGROUND: The literature contains only a few studies pertaining to strength levels of the neck rotator muscles in the neutral position. None of these studies have dealt in detail with maximal neck strength in selected prerotation positions. METHOD: Twenty healthy men volunteered as subjects. Maximal axial rotation strength of the neck muscles was measured in a neutral position and bilaterally at 30 degrees and 60 degrees rotation using the isometric neck strength measurement system. Isometric maximum voluntary contractions of the neck muscles in flexion and extension were also tested. RESULTS: The highest strength values were not reached in the neutral position, but at the largest joint angles, while turning the head in the opposite direction from the prerotated position. Maximal strength increased with increasing angle, and at the 60 degrees prerotation angle it was 44% higher towards the right and 27% higher towards the left compared to the values obtained in the neutral position. The smallest strength values were also produced at the largest prerotation angles, but in the same direction. CONCLUSIONS: The present results show a clear relationship between the prerotated position of the neck and maximal voluntary strength in rotation. RELEVANCE: The data suggest that neck strength is highly prerotation angle dependent. Neck strength should be measured at several prerotation positions in addition to the neutral position in order to obtain the true strength values throughout the entire range of motion. Maximal neck rotation strength between subjects is differentiated best at the greatest prerotation angles.

Humans↗

PubMed2003

Muscle strength, disability and mortality.

The aims of this review are to address (1) the role of muscle strength in the disablement process and (2) muscle strength as a predictor of length of life using data from prospective studies. Functional limitations, such as slow walking speed, predispose older people to disabilities. How much strength is needed for daily motor tasks such as walking varies according to other impairments present. For example, when postural balance is good, only minimum amount of strength is needed for walking. However, in the presence of balance impairment, having good level of strength may help to compensate for the deficit. Having strength well above the required level indicates reserve capacity. It was studied using data from the Honolulu Heart Program launched in 1965 among 8006 men initially aged 45-68 years, whether reserve of strength would be protective of development of future disability. All men with documented diseases at baseline were excluded from the analyses. Those men who were in the lowest third of the distribution of grip strength at baseline were at two to three times greater risk of developing disabilities assessed 25 years later compared to the highest third. It is possible that before they reach the disability level, those with greater reserve of strength may afford to lose more strength, for example following bed rest and inactivity associated with an illness. Midlife grip strength was also found to predict long-term total mortality: those with poorer strength at baseline were more likely to die over the follow-up period of 30 years. The association between muscle strength and disability is largely explained by biomechanical mechanisms. However, the mechanism explaining the association between muscle strength and mortality risk still remains to be explored.

Activities of Daily Living↗

PubMed2006

Muscle strength recovery and its effects on outcome after open reduction and internal fixation of acetabular fractures.

OBJECTIVE: To determine the relationship between muscle strength recovery and functional outcome in patients who were treated for an acetabular fracture via an anterior approach. DESIGN: Case series. SETTING: University Medical Center. PATIENTS: Fifteen patients with a displaced acetabular fracture treated via an anterior, ilioinguinal approach were studied. Hip muscle strength of these patients was then compared with the muscle strength of a similar group of patients treated via a Kocher-Langenbeck approach (posterior approach). These patient groups were then combined and muscle strength recovery was compared with the functional outcome. MAIN OUTCOME MEASURE: Primary outcome measures included hip muscle strength, including work (J/min) and maximum torque (Nm/kg) for abductors/adductors and flexors/extensors. Clinical outcome was assessed with the Musculoskeletal Function Assessment (MFA) questionnaire and the results correlated with muscle strength. Secondary outcome measures included adequacy of fracture reduction, radiographic grade, severity of heterotopic ossification, and range of motion of the affected and unaffected hips. RESULTS: At an average follow-up of 44 months, patients treated via an anterior approach had an overall muscle strength deficit of 9%. Hip extension strength was affected to the least extent (6% deficit when compared with the unaffected hip) whereas abduction, adduction, and flexion strength was affected to a greater degree. For each measure the affected side was typically weaker than the unaffected side. The average MFA score for the anterior approach group was 17 (range, 0 to 47) with most patients reporting poorest results in those domains assessing activities of the arms and legs, and those involving life changes and feelings. When MFA scores were compared with the muscle strength, a relationship was found between hip extension/flexion work and maximum torque and hip adduction work and maximum torque and MFA score. For each of these muscle groups, patients reported worsening function with decreased muscle strength. Assessment of the most recent radiographs revealed 9 patients with an excellent radiographic grade, 3 patients with a good grade, 1 patient with a fair grade, and 2 patients with a poor grade. Hip range of motion was not statistically different when the affected hip was compared with the unaffected hip, and none of these variables correlated with outcome. Heterotopic ossification was found in 8 patients; 4 with grade 1, and 4 with grade 2. CONCLUSIONS: Standardized muscle strength determination and completion of an MFA questionnaire provided a thorough evaluation of patients who had undergone open reduction and internal fixation of a displaced acetabular fracture. In these patients, hip muscle strength after operative treatment of a displaced acetabular fracture directly influences patient outcome. Therefore, in order to maximize the outcome of these patients, particular attention must be paid to postoperative muscle strengthening protocols and accurate and validated methods to assess strength and outcomes.

Acetabulum↗

PubMed1988

Cross-bridge behaviour in skinned smooth muscle of the guinea-pig taenia coli at altered ionic strength.

1. The effects of varied levels (25-300 mM) of ionic strength on mechanical properties and ATP hydrolysis rate of chemically skinned guinea-pig taenia coli fibres were investigated. 2. The tension development following activation by calcium (pCa 4.8), and relaxation following removal of calcium (pCa 9), were slower in 25 mM compared to 150 mM ionic strength. In fibres activated by thiophosphorylation of myosin light chains, by exposure to ATP-gamma-S, the tension development was rapid and independent of ionic strength. 3. The maximal shortening velocity (Vmax) was obtained from force-velocity relations determined by the quick-release method. The rate of ATP hydrolysis (JATP) was determined by measurement of pyruvate released from phosphoenolpyruvate (PEP). In order to obtain maximal Vmax and JATP at a Mg-ATP concentration of 1 mM, an ATP regenerating system was required. In thiophosphorylated fibres 2 mM-phosphocreatine (PCr) or 3.2 mM-PEP were adequate for maximal Vmax and JATP respectively. In calcium-activated fibres 5 mM-PCr was required for maximal Vmax. 4. The isometric force of thiophosphorylated fibres showed a biphasic dependence on ionic strength with a maximum at 90 mM. Vmax was essentially unchanged between 50 and 200 mM ionic strength. At 25 mM ionic strength, isometric force and Vmax were decreased by, respectively, about 15 and 25%. At 250 mM ionic strength, isometric force and Vmax were decreased by, respectively, 47 and 33%. 5. Vmax decreased with decreasing [Mg-ATP]. At [Mg-ATP] less than 0.1 mM there was no difference in Vmax between 35 and 150 mM ionic strength. At 250 mM ionic strength Vmax was lower than that at 150 mM at all [Mg-ATP]. 6. JATP during contraction in thiophosphorylated fibres at 35, 150 and 250 mM ionic strength was respectively, 0.62, 0.98 and 0.93 mumol g-1 min-1. The energetic tension cost (JATP/force) increased with ionic strength. 7. The force response to a quick stretch was investigated in the relaxed, contracted and rigor states at 25, 150 and 250 mM ionic strength. Stiffness in the relaxed state increased with speed of stretch and was higher the lower the ionic strength. In the contracted and rigor states, stiffness was also affected by ionic strength, but the relative effect in the contracted state was small.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗

PubMed2003

Quadriceps strength and osteoarthritis progression in malaligned and lax knees.

BACKGROUND: Quadriceps muscle strengthening is a common goal in the management of knee osteoarthritis. In healthy knees, strength protects against new osteoarthritis. In arthritic knees, greater strength may protect joints and thereby delay osteoarthritis progression. Alternatively, in certain joint environments, such as malalignment or laxity, greater strength may translate into damaging joint reaction forces. The relationship between quadriceps strength and progression of knee osteoarthritis may differ according to these factors. OBJECTIVE: To determine whether greater quadriceps strength is associated with greater probability of tibiofemoral osteoarthritis progression in malaligned knees and in high-laxity knees. DESIGN: Prospective, longitudinal cohort study. SETTING: Academic medical center. PARTICIPANTS: 237 persons with primary knee osteoarthritis, definite tibiofemoral osteophytes, and at least some difficulty with knee-requiring activity. Two hundred thirty completed the 18-month evaluation. The current study primarily involved those without advanced osteoarthritis in either knee (n = 171). MEASUREMENTS: Quadriceps strength, knee laxity and alignment, and osteoarthritis progression. RESULTS: The predicted probability of tibiofemoral progression was 0.153 (95% CI, 0.100 to 0.228) in high-strength knees and 0.098 (CI, 0.061 to 0.155) in low-strength knees. In malaligned knees, high strength was associated with a significant increase (P = 0.03) in the likelihood of progression (predicted probability, 0.406 [CI, 0.226 to 0.615] vs. 0.187 [CI, 0.081 to 0.375] in high-strength vs. low-strength knees). Strength was also associated with increased likelihood of progression in high-laxity knees (P = 0.003 when high laxity was defined as > or =6.75 degrees). The probability of patellofemoral progression did not differ between high- and low-strength knees in the full sample or within subsets. CONCLUSIONS: Greater quadriceps strength at baseline was associated with increased likelihood of tibiofemoral osteoarthritis progression in malaligned knees and lax knees. Subset-specific approaches beyond strengthening exercises should be developed to enhance joint-protective muscle activity.

Body Mass Index↗

PubMed2006

Sensitivity of vertebral compressive strength to endplate loading distribution.

The sensitivity of vertebral body strength to the distribution of axial forces along the endplate has not been comprehensively evaluated. Using quantitative computed tomography-based finite element models of 13 vertebral bodies, an optimization analysis was performed to determine the endplate force distributions that minimized (lower bound) and maximized (upper bound) vertebral strength for a given set of externally applied axial compressive loads. Vertebral strength was also evaluated for three generic boundary conditions: uniform displacement, uniform force, and a nonuniform force distribution in which the interior of the endplate was loaded with a force that was 1.5 times greater than the periphery. Our results showed that the relative difference between the upper and lower bounds on vertebral strength was 14.2 +/- 7.0% (mean +/- SD). While there was a weak trend for the magnitude of the strength bounds to be inversely proportional to bone mineral density (R2 = 0.32, p = 0.02), both upper and lower bound vertebral strength measures were well predicted by the strength response under uniform displacement loading conditions (R2 = 0.91 and R2 = 0.99, respectively). All three generic boundary conditions resulted in vertebral strength values that were statistically indistinguishable from the loading condition that resulted in an upper bound on strength. The results of this study indicate that the uncertainty in strength arising from the unknown condition of the disc is dependent on the condition of the bone (whether it is osteoporotic or normal). Although bone mineral density is not a good predictor of strength sensitivity, vertebral strength under generic boundary conditions, i.e., uniform displacement or force, was strongly correlated with the relative magnitude of the strength bounds. Thus, explicit disc modeling may not be necessary.

Aged↗

PubMed2003

Five years of growth hormone replacement therapy in adults: age- and gender-related changes in isometric and isokinetic muscle strength.

GH replacement therapy in adults with adult-onset GH deficiency (GHD) has been shown to increase isometric and isokinetic muscle strength in a few trials with limited numbers of patients. In this single center, prospective, open-label study, the effects of 5-yr GH replacement therapy on muscle function were determined in 109 consecutive adults (61 men and 48 women) with adult-onset GHD. The mean initial GH dose was 0.88 mg/d. The dose was gradually lowered, and after 5 yr the mean dose was 0.46 mg/d. The mean IGF-I SD score increased from -1.54 at baseline to 1.53 at study end. A sustained increase in lean body mass and decrease in body fat was observed. The GH treatment induced persistent increases in isometric knee flexor strength, concentric knee flexor strength at an angular velocity of 60 degrees/sec, and right-hand peak grip strength. After correction for age and gender using observed/predicted value ratios, a sustained increase was also observed in isometric (60 degrees) and concentric (180 degrees/sec) knee extensor strength, average right-hand grip strength for 10 sec, and left-hand grip strength. At study end, knee flexor and extensor strength was 96-104% of predicted and hand grip strength was 84-90% of predicted values. The local muscle endurance was transiently decreased after correction for age and gender. No gender difference was found in the treatment responses in muscle strength. However, muscle strength (also after correction for age and gender) was lower in women than men throughout the study period. In conclusion, GH replacement therapy in adults with adult-onset GHD normalized isometric and isokinetic knee flexor and extensor strength. Hand grip strength increased but was not fully normalized.

Adipose Tissue↗

PubMed1997

Two years of growth hormone (GH) treatment increase isometric and isokinetic muscle strength in GH-deficient adults.

GH deficiency in adults is associated with reduced muscle mass and muscle strength. The objective of this trial was to follow the effect of 2 yr of GH treatment in GH-deficient adults on muscle performance in relation to a reference population. Knee extensor and flexor strengths for isometric and isokinetic concentric muscle strength were measured using a Kin-Com dynamometer. Hand-grip strength was measured in both hands. The fatigue index was calculated as the percent reduction in peak torque at 50 repeated isokinetic knee extensions. Superimposed, single twitch electrical stimulation was performed. The GH-deficient subjects had lower isometric knee extensor, knee flexor, and hand-grip strength than the reference population. Two years of GH treatment increased and normalized the mean isometric knee extensor and flexor strengths. The concentric knee flexor and extensor strength at an angular velocity of pi rad/s increased, as did the concentric knee flexor strength at an angular velocity of pi/3 rad/s. The increase in muscle strength was more marked in younger patients and in patients with lower initial muscle strength than predicted. Quadriceps endurance decreased, whereas the effect of superimposing single twitches on isometric contraction and hand-grip strength was unaffected by the GH treatment. Two years of GH therapy in GH-deficient adults increased and normalized isokinetic and isometric muscle strength studied in proximal muscle groups. Hand-grip strength and the degree of lack of maximal motor unit activation on voluntary isometric knee extensor force did not change. The dynamic local muscle fatigue index decreased.

Adult↗

PubMedDate not supplied

Grip and pinch strength in relation to function in denervated hands.

A study was conducted in the Schieffelin Leprosy Research and Training Centre, Karigiri, Tamil Nadu, from March to September 2000 to find out the relationship between grip and pinch strengths and basic activities of daily living (BADL) in leprosy patients. Sixty-two patients (mean age: 36.1 years) suffering from impairment of motor nerve function in one or both hands were included in the study. Grip strength and pinch strength, namely pulp-to-pulp pinch strength, lateral pinch strength, tripod pinch strength, were measured using a hydraulic hand dynamometer and a pinch gauge. BADL was assessed using Karigiri activities of daily living rating scale. Frequency table, mean, median, range, standard deviation, correlation and multiple regressions were used in analysis. The results showed that there was a highly significant correlation (p < 0.001) between the grip and pinch strength and BADL. Multiple regression analysis showed only tripod pinch strength had a significant, independent influence on the BADL. Other two pinch strengths and grip strength were not significant. These results suggest that there is a significant relationship between the grip and pinch strengths and BADL. The tripod pinch strength is the most important hand strength contributing to the problems in BADL. In a measure of association between impairment and disability, the results revealed that out of 62 patients with physical impairment of the hand, 59 (95.2%) had experienced disabilities. This indicated that, despite impairment, 4.8% do not have any disabilities.

Activities of Daily Living↗

PubMed2004

The dependence between the strength and stiffness of cancellous and cortical bone tissue for tension and compression: extension of a unifying principle.

A strong positive correlation between the apparent ultimate strength and stiffness of bone tissue that can be expressed by a unified relationship has been observed for cortical bone in tension and low-density cancellous bone in compression. For practical purposes, the existence of a relationship between strength and stiffness is significant in that bone stiffness can be measured in vivo using non-invasive methods. It is generally accepted that bone strength is greater in compression than in tension whereas there is no substantial evidence that bone stiffness in compression is different from that in tension. This might suggest that compressive strength would relate to the stiffness, if at all, in a way that is different from tensile strength. In order to examine similarities and differences in the way strength is associated with stiffness between modes of loading and tissue type, we tested equine cortical bone and bovine cancellous bone in compression and examined these data together with previously reported data from compression testing of human cancellous bone as well as tensile testing of cortical bone from various sources. We have found for cortical bone that (i) the sensitivity of strength to stiffness is the same for tension and compression (p>0.75, ANCOVA), and (ii) the difference between the magnitudes of compressive and tensile strength for cortical bone is the result of an additive, rather than a multiplicative factor (52.1 MPa after adjusting to 1 microstrain/s, p<0.0001, ANOVA). High-density bovine tibial cancellous bone, on the other hand, has a steeper slope for its compressive strength-stiffness relationship than that for cortical bone and human cancellous bone, resulting in a transitional relationship between compressive strength and stiffness for a range of bone types and densities. Based on the current results and previous work, it is suggested that the offset strength in the compressive strength-stiffness relationship may be a direct manifestation of the difference between the compressive and tensile strengths of the bone material that constitutes the building blocks of the bone structure. Deviation of high-density cancellous bone compressive behavior from the other bone types and densities is attributed to stress distribution differences between the bone types.

Adaptation, Physiological↗

PubMed2001

Lymphocyte proliferation in response to acute heavy resistance exercise in women: influence of muscle strength and total work.

Little is understood about the immune responses to heavy resistance exercise. The purpose of this investigation was to determine the influence of physical strength and the ability to do more total work on lymphocyte proliferation after an acute bout of heavy resistance exercise. A group of 50 healthy but nonstrength trained women were recruited for the study and tested for their one repetition maximum (i.e. 1 RM or maximal mass lifted once). From the normal distribution of strength the top and bottom 8 women [mean age 22.5 (SD 3.1) years] were asked to volunteer to define our two groups (i.e. high strength and low strength). The two groups were significantly different (P < 0.05) in 1 RM squat strength [low strength 39.9 (SD 4.6) kg, 0.65 (SD 0.08) kg.kg body mass-1 and high strength 72.2 (SD 10.7) kg, 1.1 (SD 0.12) kg.kg body mass-1] but were not significantly different in body mass, age, activity levels, and menstrual status (all in same phase). Each performed a resistance exercise protocol consisting of six sets of 10 RM squats with 2 min rest between the sets. The 10 RM loads and total work were significantly greater in the high strength group than in the low strength group. Blood samples were obtained pre-exercise and immediately post-exercise for test for lactate (significant increase with exercise) and cortisol (no changes) concentrations with no differences noted between groups. Immunological assays on the blood samples determined the incorporation of tritiated thymidine by lymphocytes in responses to concanavalin A (ConA), phytohemagglutinin (PHA), and pokeweed mitogen (PWM). Following the squat exercise, there was a significant decrease in lymphocyte responsiveness to PWM in the high strength but not in the low strength group for both total proliferation and proliferation adjusted per B or T cell. On the other hand, lymphocytes from the low strength group proliferated to a significantly greater extent (adjusted per T cell) in response to ConA and PHA. These data indicate that the heavy resistance exercise protocol reduced the lymphocyte proliferative responses only in the stronger group of subjects. This effect may have been due to the high absolute total work and the greater exercise stress created by the resistance exercise protocol in the high strength group. Therefore, individuals performing at the same relative exercise intensity (i.e. 10 RM) in a resistance exercise protocol may have different immune responses stemming from differences in absolute total work performance.

Adult↗

PubMed1998

The effect of ionic strength on the kinetics of rigor development in skinned fast-twitch skeletal muscle fibres.

Recent atomic 3-D reconstructions of the acto-myosin interface suggest that electrostatic interactions are important in the initial phase of cross-bridge formation. Earlier biochemical studies had also given strong evidence for the ionic strength dependence of this step in the cross-bridge cycle. We have probed these interactions by altering the ionic strength (Gamma/2) of the medium mainly with K+, imidazole+ and EGTA2- to vary charge shielding. We examined the effect of ionic strength on the kinetics of rigor development at low Ca2+ (experimental temperature 18-22 degrees C) in chemically skinned single fast-twitch fibres of mouse extensor digitorum longus (EDL) muscle. On average the delay before rigor onset was 10 times longer, the maximum rate of rigor tension development was 10 times slower, the steady-state rigor tension was 3 times lower and the in-phase stiffness was 2 times lower at high (230 mM) compared to low (60 mM) ionic strength. These results were modelled by calculating ATP depletion in the fibre due to diffusional loss of ATP and acto-myosin Mg.ATPase activity. The difference in delay before rigor onset at low and high ionic strength could be explained in our model by assuming a 15 times higher Mg.ATPase activity and a threefold increase in Km in relaxing conditions at low ionic strength. Activation by Ca2+ induced at different time points before and during onset of rigor confirmed the calculated time course of ATP depletion. We have also investigated ionic strength effects on rigor development with the activated troponin/tropomyosin complex. ATP withdrawal at maximum activation by Ca2+ induced force transients which led into a "high rigor" state. The peak forces of these force transients were very similar at low and high ionic strength. The subsequent decrease in tension was only 10% slower and steady-state "high rigor" tension was reduced by only 27% at high compared to low ionic strength. Addition of 10 mM phosphate to lower cross-bridge attachment strongly suppressed the transient increases in force at high ionic strength and reduced the steady-state rigor tension by 17%. A qualitatively similar but smaller effect of phosphate was observed at low ionic strength where steady-state rigor force was reduced by 10%. The data presented in this study show a very strong effect of ionic strength on rigor development in relaxed fibres whereas the ionic strength dependence of rigor development after thin filament activation was much less. The data confirm the importance of electrostatic interactions in cross-bridge attachment and cross-bridge-attachment-induced activation of thin filaments.

Adenosine Triphosphate↗

PubMed1993

Trabecular bone modulus and strength can depend on specimen geometry.

We performed a series of uniaxial compression tests on wet bovine trabecular bone to compare both modulus and strength when measured using 2:1 aspect ratio (10 mm long, 5 mm diameter) cylinders (n = 30) and 5 mm cubes (n = 29). We also compared the correlation coefficients in the resulting modulus-density and strength-density regressions and the standard errors of the estimate. When comparing the mean values of modulus and strength for each group, the confounding variations in apparent density were accounted for with an analysis of covariance. The Fisher's Z transformation was used to compare the correlation coefficients statistically. Results from the analysis of covariance indicated that the modulus and strength of the cubes were higher by 36% (p < 0.01) and 18% (p < 0.05), respectively, with respect to the 2:1 cylinder values. The correlation coefficients in the modulus-density and strength-density regressions were not sensitive to the regression model (linear versus power law). However, correlation coefficients for both modulus-density and strength-density regressions were higher (p < 0.05) for the 2:1 cylinders (r = 0.90, modulus; r = 0.94, strength) than for the cubes (r = 0.57, modulus; r = 0.82, strength). In addition, the standard errors of the estimate in both modulus and strength were substantially lower for the 2:1 cylinders. These data indicate that both modulus and strength can depend on the specimen geometry when using conventional compression testing techniques. We conclude, therefore, that inter-study comparisons of modulus and strength may be invalid if these confounding effects of different specimen geometries are not addressed. Our data also indicate that density can better explain the observed variance in modulus and strength when 2:1 cylinders are used as opposed to cubes. Using this phenomenon as a rationale for choosing a standard specimen gometry, we recommend that the 2:1 cylinder be used as a standard specimen in studies designed to determine the effects of various treatments on the uniaxial compressive modulus and strength of trabecular bone.

Animals↗

PubMed1998

Is lower extremity strength gain associated with improvement in physical performance and disability in frail, community-dwelling elders?

BACKGROUND: Strength loss is strongly associated with functional decline and is reversible with exercise. The effect of increased strength on function has not been clearly established. The purpose of this study was to determine whether strength gain is associated with improvement in physical performance and disability. METHODS: One hundred functionally impaired community-dwelling men and women (77.6 +/- 7.6 yrs) were tested at baseline and outcome for lower extremity strength, physical performance, and disability. After random group assignment, exercise participants received strengthening exercises in their homes three times a week for 10 weeks while control subjects continued their normal activities. Using multiple regression techniques, the relationship between strength gain and improvement in physical performance and disability was assessed, controlling for age, depression, and baseline strength. RESULTS: A significant impact of strength gain on mobility skills (p = .0009) was found. The impact of strength gain on chair rise performance was significant in participants who were more impaired (p = .04). Strength gain was associated with gain in gait speed (p = .02) and in falls efficacy (p = .05), but not with other balance, endurance, or disability measures. CONCLUSIONS: Lower extremity strength gain is associated with gains in chair rise performance, gait speed, and in mobility tasks such as gait, transfers, stooping, and stair climbing, but not with improved endurance, balance, or disability. Strength gain is also associated with improvement in confidence in mobility. Factors that may influence the ability of strength gain to affect function are initial level of frailty and specificity of exercise. These results support the idea that strength training is an intervention that can potentially improve physical health status in many frail elders.

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