Peak Isometric Force Research Articles

Effects Of Six Weeks Periodized Squat Training With Or Without Whole Body Vibration Upon The Relationship Between Isometric And Dynamic Performance

Resistance training interventions aimed at increasing lower body power and rates of force development have produced varying results. Potentially, the use of WBLFV in between sets of resistance training may increase high-threshold motor unit recruitment and synchronization leading to greater adaptations in both isometric and dynamic performance. The relationship between isometric force/time characteristics and dynamic performance and their respective changes in response to resistance training is of practical importance to strength and conditioning practitioners. To determine the effects of applying whole body vibration prior to and then intermittently between sets of Smith Machine squats upon training induced changes in isometric and dynamic performance and their relationships to one another. Twenty four recreationally resistance trained men were randomly assigned to one of two groups, resistance only (SQT n = 11), or resistance plus whole body vibration (SQTV n = 13). An isometric squat test as well as Squat Jumps (SQJ) and Depth Jumps (DJ) were performed prior to, and following a six-week, periodized Smith Machine squat program. WBLFV was applied 180 s prior to the first work set (50Hz 2-4mm, 30 s) and intermittently (50Hz 4-6mm, 3 × 10 s, 60s between exposures) within a 240s inter-set rest period. Subjects were instructed to assume a quarter squat posture while positioning their feet directly under their center of mass which was modified using a hand held goniometer to a knee angle of 135 ± 5°. Measures of isometric force (N) and isometric rates of force development (N·s−1) were recorded from the onset of contraction (F0) to time points corresponding to F30ms, F80ms, F250ms, Force at initial peak (Finitial), Force at 50% of MVC (MVC50) Time Finitial (ms) as well as the Peak Isometric Force (MVCp) and Peak Isometric Rate of Force Development (PISORFD). Squat jumps were performed with a 20kg Olympic barbell with a linear position transducer attached while the DJ utilized body mass as resistance while dropping from a height of 30cm onto a switch mat. Measures recorded during jumps included jump height (cm) peak power (PMax,W), peak power per kg of body mass (PMax/kg, W/kg) and mean power (Pav,W) for both jump conditions. Correlation matrices matching isometric force/time variables and dynamic (SQJ, DJ) performance within group between weeks 1 and 7(Pre- Post training) revealed multiple significant positive, and negative correlations (p = *<.05 and**<.001, range, r = −.624 to .859). A greater total amount of positive correlations were seen for SQTV (24) compared to SQT (2). Correlation coefficients (r) calculated between percent change (%Δ) scores for similar variables revealed small to moderate r values with the only significant correlation seen for the SQTV group between F30ms and DJ height (cm) (r = −.589, R2 = −.347, p <.05). More positive correlations were seen for isometric and dynamic %Δ variables that for SQTV (9) compared to SQT (7). The addition of WBLFV to the SQTVgroup appeared to effect neuro-muscular training adaptation differently from SQT as reflected in the percent change relationship between isometric and dynamic performance measures following six weeks of exposure. WBLFV may help facilitate early phase adaptations to resistance exercise with a tendency to improve early force time components of isometric and dynamic performance.

Contraction-Mediated Damage in mdx Mice Trabeculae: A Model for Cardiomyopathy in Duchene Muscular Dystrophy

Duchene muscular dystrophy (DMD) is an inherited and progressive disease of striated muscle deterioration. Studies on skeletal muscle using an eccentric contraction model have provided great insight of the contraction-mediated damage in skeletal muscle in DMD. Because of different contraction mechanics in the cardiac vs. skeletal muscle, the protocols used to gain understanding in skeletal muscle pathology cannot be readily applied to the myocardium. To investigate contraction-mediated damage in dystrophin-deficient myocardium under physiological conditions, we developed an in vitro model of myocardial mechanics-induced injury. We employed computer-programmed protocols to trigger consecutive lengthening ramps during the twitch contraction at 4 Hz in age matched (young and adult) mdx and wild type mice right ventricular trabeculae. These ultra-thin muscles possess all major cardiac cell types and their contractile behavior very closely mimics that of the whole heart. In the first group of experiments, 10 lengthening contractions of various (1-10%) magnitude of stretch were performed in trabeculae from 10 week old mdx and wild type mice. In the second group, 100 lengthening contractions at each magnitude were conducted in trabeculae from 20 weeks old mice. The peak isometric active developed tension (Fdev, in mN/mm2), diastolic tension (Fdia), and force kinetics were measured throughout the protocol, and the rate of decline of these parameters can be taken as a relative measurement of how susceptible the myocardium is to lengthening-induced dysfunction. Our results indicate dystrophin deficient myocardium in older mdx mice is more sensitive to severe mechanical stress compared to age-matched wild type controls. This suggests that lengthening contraction in myocardium is an appropriate model to study contraction-mediated damage in DMD associated cardiomyopathy.

Relationship Between Strength Characteristics and Unweighted and Weighted Vertical Jump Height

To investigate the relationship between maximum strength and differences in jump height during weighted and unweighted (body weight) static (SJ) and countermovement jumps (CMJ). Sixty-three collegiate athletes (mean +/- SD; age= 19.9 +/- 1.3 y; body mass = 72.9 +/- 19.6 kg; height = 172.8 +/- 7.7 cm) performed two trials of the SJ and CMJ with 0 kg and 20 kg on a force plate; and two trials of mid-thigh isometric clean pulls in a custom rack over a force plate (1000-Hz sampling). Jump height (JH) was calculated from flight time. Force-time curve analyses determined the following: isometric peak force (IPF), isometric force (IF) at 50, 90, and 250 ms, and isometric rates of force development (IRFD). Absolute and allometric scaled forces, [absolute force/(body mass(0.67))], were used in correlations. IPF, IRFD, F50(a), F50, F90, and F250 showed moderate/strong correlations with SJ and CMJ height percent decrease from 0 to 20 kg. IPF(a) and F250(a) showed weak/moderate correlations with percent height decrease. Comparing strongest (n = 6) to weakest (n = 6): t tests revealed that stronger athletes (IPF(a)) performed superior to weaker athletes. Data indicate the ability to produce higher peak and instantaneous forces and IRFD is related to JH and to smaller differences between weighted and unweighted jump heights. Stronger athletes jump higher and show smaller decrements in JH with load. A weighted jump may be a practical method of assessing relative strength levels.

Vitamin E and C supplementation does not ameliorate muscle dysfunction after anterior cruciate ligament surgery

Muscle atrophy and weakness are predominant impairments after anterior cruciate ligament (ACL) surgical repair. We tested the hypothesis that vitamin E and C supplementation will improve recovery from ACL injury. Men undergoing elective ACL surgery were randomly assigned to twice-daily supplements of either antioxidants (AO; vitamins E and C, n = 10) or matching placebos ( n = 10) from 2 weeks before until 3 months after surgery. Each subject provided several fasting blood draws, two muscle biopsies from the thigh muscle of the injured limb, and strength and thigh circumference measurements of the lower limbs. Muscle atrophy was apparent in both groups before and several days after surgery. Compared with baseline measurements, peak isometric force of the injured limb increased significantly ( P < 0.05) by 3 months postsurgery in both treatment groups; however, AO supplementation did not augment these strength gains. By contrast, baseline plasma ascorbic acid concentrations correlated ( r = 0.59, P = 0.006) with subsequent improvement in the strength of the injured limb. In summary, vitamin E and C supplementation was ineffective in potentiating the improvement in force production by the injured limb; however, baseline vitamin C status was associated with beneficial outcomes in strength, suggesting that long-term dietary habits are more effective than short-term supplements.

Variation Between Repeated Time-To-Exhaustion Trials Reduced With Utilization Of An Objective Exclusion Criteria.

PURPOSE: Time to exhaustion (TTE) protocols are widely used to assess endurance performance. However, the subjective endpoint of this method can contribute to increased variance between trials. Our purpose was to determine if an objective criteria for determining successful TTE completion reduced error variance between repeated trials. METHODS: Ten recreational exercisers (age = 24±5 yrs; VO2max = 53.6±9.9 mL·kg-1·min-1) completed a TTE protocol consisting of a 75 minute cycle at 70% VO2max followed by a treadmill run to exhaustion at 80% VO2max. Subjects completed two TTE trials. In trial 1, all subjects were instructed to run until volitional exhaustion. In Trial 2, five subjects were similarly instructed to provide a maximal effort until exhaustion (ME). The other 5 subjects received instructions to cease running when they estimated they could complete only 10 additional minutes of exercise (SME). Peak isometric force (MVC) of the leg extensors was assessed pre-exercise and immediately post-exercise. An objective MVC criteria was used to exclude subjects who did not successfully complete the TTE trials. Subjects TTE data was excluded if their MVC declined <10% from pre-exercise levels, and their lowest MVC decline occurred in their shortest TTE trial. RESULTS: Prior to application of the exclusion criteria, there was a relatively low correlation (r=0.31) and high variation (CV=34.2%) between repeated trials, partially due to the inconsistent efforts of the SME group. The exclusion criteria eliminated three subjects from the analysis, which improved the correlation (r=0.61) and CV (24.3%) between trials. DISCUSSION: The MVC criteria correctly eliminated the two subjects with the greatest variance between TTE trials, and significantly reduced the total error variance between trials. Thus, using % MVC decline as an objective TTE completion criteria' may reduce error variance by identifying subjects who are unable to provide consistent efforts between trials. Refinement of the existing criteria may result in further improvement in consistency between trials, as not all SME trials were identified by the present criteria.

Effects Of Olive Extract Supplementation On Post-exercise Markers Of Muscle Recovery

PURPOSE: Olive extract (OE) is derived from the aqueous fraction of olives and is rich in polyphenols, including the potent antioxidant hydroxytyrosol (HT). Previous studies have shown that olive poyphenols can confer antioxidant protection in vivo, as shown by increased plasma total antioxidant capacity and protection against LDL oxidation. Antioxidants may affect muscle recovery following strenuous exercise. The purpose of this study was to determine if OE supplementation influenced plasma creatine kinase (CK), muscle soreness, and muscle function following heavy aerobic exercise. METHODS: 19 male subjects (21.2±2.9 yr, 23.9±1.7 BMI) underwent 3 treatment phases, consisting of 14-day supplementation periods with either 0 mg OE/d (placebo: PL), 400 mg OE/d (OE-400), or 800 mg OE/d (OE-800), administered in two daily doses providing a total of 8 and 16 mg HT, respectively. The exercise bout included 100 minutes of ergometer cycling at 60% VO2peak, followed by 20 minutes of treadmill running at 70%VO2peak. Plasma CK levels, muscle soreness ratings and peak isometric force (MVC) of the leg-extensors were obtained prior to the supplementation period (BL), pre-exercise, immediately post-exercise (0-PO), 2 hours post-exercise (2-PO) and 24 hours post-exercise (24-PO). A 12-day washout period separated the treatment phases, which were administered in a double-blind design. RESULTS: Following supplementation, total area under the curve (AUC) for HT was significantly greater for OE-800 versus OE-400 and PL. HT AUC was also significantly greater with OE-400 versus PL. Plasma CK levels rose significantly from pre- (273.4±310.6 U/L) to post-exercise (peak at 24-PO: 429.2±381.5 U/L). Muscle soreness also increased from pre- (14.5±9.6 mm) to post-exercise (peak at 0-PO: 50.7±20.0 mm). MVC declined significantly from pre-exercise (574.3±165.3 N) to post-exercise (0-PO: 524.0±169.7 N). No treatment*time interactions or differences in AUC were observed for muscle recovery variables. CONCLUSION: OE supplementation significantly increased plasma HT concentrations, but did not affect plasma CK levels, muscle soreness or muscle function following heavy aerobic exercise. Further study is required to determine if higher doses of OE elicit positive effects on these variables.

Does vitamin D status predict outcomes of experimentally‐induced muscle pain and weakness in healthy young volunteers?

Vitamin D receptor's presence in skeletal muscle indicates a role in muscle function and clinical symptoms of vitamin D deficiency include muscle weakness and pain. No one has yet examined the association of vitamin D status and experimentally‐induced muscle pain or weakness in healthy people.MethodsMuscle damage to the elbow flexors was induced with eccentric exercise (EE) in 27 men (mean age 22.5 yr) and 21 women (mean age 22.6 yr). Muscle pain ratings from unloaded movement and isometric contractions and peak isometric force (IF) were collected before EE and for 4 days post‐EE. Serum 25‐hydroxy vitamin D (25OHD) was assayed 2 days post‐EE. Linear regression was used to determine if 25OHD was a predictor of any outcome.ResultsSerum 25OHD did not predict any of the pain or strength measures. In men: R2 for pain ratings ranged from 0 to 0.02, and p‐values from 0.48 to 1.00. R2 for IF ranged from 0 to 0.02 and p‐values from 0.48 to 1.00. In women: R2 for pain ratings ranged from 0.01 to 0.21, and p‐values from 0.14 to 0.74 . R2 for IF ranged from 0 to 0.04 and p‐values from 0.41 to 0.90.ConclusionSerum 25OHD did not predict muscle pain or strength after EE‐induced muscle damage in young healthy men and women. Support: Dept. of Nutritional Sciences, Univ. of Missouri, CA Peterson; and National Institute of Arthritis and Musculoskeletal and Skin Diseases (KO1 AR050146) and the Univ. of Missouri, EA Dannecker.

X-Ray Diffraction “Movie” Of Complete Oscillatory Work Cycles Myogenically Produced In Glycerinated Insect Flight Muscle (IFM)

When slightly calcium-activated (pCa ∼5.7, gives ∼0.2 peak isometric force), glycerinated Lethocerus insect flight muscle (IFM) can be mechanically stretch-activated at constant [Ca2+] to give a delayed active rise to peak force, a myogenic response typical of asynchronous IFM. Continuous sine-wave length-oscillations elicit sinusoidally cycling force traces, delayed ∼45° behind length cycles. Force-length x-y plots therefore follow anti-clockwise Lissajous loops of elliptical form, enclosing an area proportional to oscillatory work output per cycle, which peaked at ∼2%X∼2Hz for 10-20-fiber bundles. A Pilatus 100K detector collected 64 synchrotron-x-ray fiber-diffraction frames per full cycle (8ms time resolution), throughout an 11-cycle run (704 frames). Summing successive cycles and adjacent frames produced a 16-frame movie (32ms time resolution) showing weaker details. The movie shows clear within-cycle peak-to-valley intensity changes in multiple reflections, some signaling crossbridge mass shifts toward (and away from) thin-filament lattice positions, others crossbridge shifts between binding to and detaching from actin target zones, still others signaling crossbridge shifts between tilt angles mostly near 90° versus mostly dispersed to non-90° angles. Surprises include: 1) Maximum 90° angles occur near force peak in Drosophila but near force valley in Lethocerus. 2) Although the force sine-wave varies smoothly, two structural signals of crossbridge attachment show biphasic profiles as force rises and again as force falls, as if outer and inner myosin heads (AL-Khayat etal model) attach/detach in separate cohorts during the 2% (26 nm/half-sarcomere) length changes. 3) Structural signals of crossbridge action are variably phase-coupled to the force sine-wave; some x-ray signals even differ in phase lag between force peak and valley. Maximum tropomyosin shift spans ∼5 frames around force peak. Overall results strongly constrain possible mechanisms of stretch-activation, suggesting complementary approaches for revealing it. (Support: NIH, DOE).

Typing keystroke duration changed after submaximal isometric finger exercises

A repeated-measures laboratory experiment tested whether keystroke duration during touch-typing changes after a finger performs submaximal isometric flexion exercises. Fourteen right-handed touch-typists used right ring finger to perform three 15-min exercise conditions, two isometric exercises and a no-force condition, each on a separate day. Before and after each exercise condition, typing keystroke duration and isometric force elicited by electrical stimulation were measured for right ring finger. Keystroke duration of right ring finger decreased by 5% (6 ms, P < 0.05) immediately after the exercises but not after the no-force condition. Peak isometric finger force elicited by electrical stimulation decreased by 17-26% (P < 0.05) for the flexor digitorum superficialis and decreased by 4-8% for the extensor digitorum communis after the isometric exercises. After the finger was exposed to isometric exercises, changes in typing keystroke duration coincided with changes in the physiological state of the finger flexor and extensor muscles.

Force-Time Curve Characteristics and Hormonal Alterations During an Eleven-Week Training Period in Elite Women Weightlifters

The purpose of this investigation was to study the effects of an 11-week training period performed by female weightlifters. Two weeks before this investigation, baseline measures for total testosterone, cortisol, and testosterone:cortisol ratio were collected. The 11-week training program consisted of the core exercises (i.e., clean, clean and jerk, and snatch) and other supplemental exercises (i.e., clean pull, snatch pull, squat, and front squat). Hormonal, isometric, and dynamic middle thigh pull force-time curve characteristics were assessed biweekly throughout the duration of the investigation, whereas volume load and training intensity were assessed weekly throughout the investigation. The testosterone:cortisol ratio of the baseline (1.19 +/- 0.64) was significantly different from the ratio of weeks 1 (0.67 +/- 0.36) and 9 (0.94 +/- 0.66). When the week-to-week values were compared, week 1 (0.67 +/- 0.36) was significantly different (P < 0.05; eta = 0.84) from week 3 (1.06 +/- 0.54). A very strong correlation (r = -0.83; r = 0.69) was found between the percentage change of the testosterone:cortisol ratio and volume load from weeks 1 to 11. Moderate to very strong correlations were noted between the percentage change in volume load and isometric peak force, peak force during the 30% isometric peak force trial, and peak force during the 100-kg trial during the 11 weeks of training. The primary finding of this study was that alterations in training volume load can result in concomitant changes in the anabolic-to-catabolic balance, as indicated by the testosterone:cortisol ratio, and the ability to generate maximal forces.

Brain activity is similar during precision and power gripping with light force: An fMRI study

Handgrips can be broadly classified into precision and power grips. To compare central neuronal control of these tasks, functional magnetic resonance imaging was used in 14 healthy right-handed volunteers, who repetitively squeezed non-flexible force transducers with a precision grip and a power grip of the dominant hand. The relative grip force levels and movement rates (0.45 Hertz) of both tasks were comparable. Peak isometric grip forces ranged between 1% and 10% of the maximum voluntary force. Reflecting the additional recruitment of extrinsic hand muscles and the higher absolute force, activation of the contralateral primary sensorimotor cortex (M1/S1) and ipsilateral cerebellum was significantly stronger during power than during precision grip. No brain areas exhibited stronger activity during the precision grip than during the power grip. The left M1/S1 and right cerebellum showed a positive linear relationship with the grip force, while the right angular gyrus and left superior frontal gyrus showed a gradual increase in activity when less force was applied. However, these force-dependent modulations of brain activity were similar for the precision and power grip tasks. No brain region was specifically activated during one task but not during the other. Activity during precision gripping did not exceed the activity associated with power gripping possibly because the precision grip task was not challenging enough to call on dexterous fine motor control.

Force-time parameters during explosive isometric grip correlate with muscle power

Although explosive isometric contraction provides little work toward the outside, force-time parameters of the rising phase of the force-time curve may be able to predict muscle power. The purpose of this study was to examine the relationship between muscle power with work (power grip) and force-time parameters during the rising phase in explosive isometric grip. Fifteen healthy young adult males participated in this study. Power grip was measured using loads of 20%–50% of maximal voluntary contraction (MVC) (peak isometric force). Subjects pulled explosively on a grip bar held with the second digital joints without the thumb. Peak power was calculated from peak velocity and load. Explosive isometric grip was measured using a hand dynamometer. Time-series data of both tests were sampled by an analog-to-digital interface. Both tests were performed with the subjects seated with a sagittal and horizontal position of the arm supported by an armrest. Peak power in the power grip test tended to be larger with an increase of the load, but there was no significant difference between 40% and 50% MVC. Only the peak power in 50% MVC significantly correlated with peak grip force (r=0.52, p<0.05). The force-time parameters related to the peak rate of the rising force phase in explosive isometric grip significantly correlated with the peak powers (30%–50% MVC, r=|0.58−0.78|). Peak rate of the rising force phase in explosive isometric grip may be useful for predicting muscle power with loads between 30%–50% MVC.

Relative shortening velocity in locomotor muscles: turkey ankle extensors operate at low V/Vmax

The force-velocity properties of skeletal muscle have an important influence on locomotor performance. All skeletal muscles produce less force the faster they shorten and typically develop maximal power at velocities of approximately 30% of maximum shortening velocity (V(max)). We used direct measurements of muscle mechanical function in two ankle extensor muscles of wild turkeys to test the hypothesis that during level running muscles operate at velocities that favor force rather than power. Sonomicrometer measurements of muscle length, tendon strain-gauge measurements of muscle force, and bipolar electromyographs were taken as animals ran over a range of speeds and inclines. These measurements were integrated with previously measured values of muscle V(max) for these muscles to calculate relative shortening velocity (V/V(max)). At all speeds for level running the V/V(max) values of the lateral gastrocnemius and the peroneus longus were low (<0.05), corresponding to the region of the force-velocity relationship where the muscles were capable of producing 90% of peak isometric force but only 35% of peak isotonic power. V/V(max) increased in response to the demand for mechanical power with increases in running incline and decreased to negative values to absorb energy during downhill running. Measurements of integrated electromyograph activity indicated that the volume of muscle required to produce a given force increased from level to uphill running. This observation is consistent with the idea that V/V(max) is an important determinant of locomotor cost because it affects the volume of muscle that must be recruited to support body weight.

Modeling of skeletal muscle: the influence of tendon and aponeuroses compliance on the force–length relationship

The aim of this study was to investigate the influence of changing elastic properties of tendon and aponeuroses on force production and muscle geometry. A three-dimensional, structural, continuum mechanics model of the cat medial gastrocnemius was used for this purpose. Increasing compliance in tendon and aponeuroses caused a decrease in the peak isometric force and a shift of the force-length relationship to the right of the length axis (i.e. toward greater muscle lengths). This result can be explained with the stability condition of the force-length relationship which produced a history dependence of force production that is conceptually in agreement with experimental observations.

Isotonic muscle function is selectively reduced after muscle damage induced by isometric exercise at a long muscle length

This study investigated the hypothesis that isotonic muscle performance following mild muscle damage would be disproportionately affected when measured at different parts of the range of motion. Seven male volunteers performed 50 maximal isometric contractions with the elbow flexors at a lengthened position. Maximal isotonic performance was measured before and for four days post-exercise at two parts of the range of motion of elbow flexion, including mainly the descending (L) or the ascending limb (S) of the angle-force curve. On day 1 post-exercise, muscle damage was evidenced by a decrease in peak isometric force (-20.3 ± 2.7%, p < 0.01), a shift in optimum angle for force generation towards a greater elbow angle (by 0.12 ± 0.03 rad, p < 0.05), and an increase in serum creatine kinase activity and muscle soreness (P < 0.01). Isotonic performance indices were decreased only in the S condition (p < 0.01). Shift in optimum angle and isotonic performance indices recovered on day 2. The disproportionate decrease in isotonic performance in the S condition may be explained by the shift of the optimum angle towards a longer muscle length, which would benefit force generation at elbow angles beyond the optimum angle but impair force at the more acute elbow angles.

Age Affects Skeletal Muscle Response to an Acute Exposure of Stretch-Shortening Contractions

Previous studies have shown that aging increased susceptibility to contraction-induced injury in skeletal muscle and impaired recovery after injury. PURPOSE: To investigate the effect of an acute stretch-shortening contraction (SSC) exposure on the temporal skeletal muscle response of young and old rats. METHODS: The left dorsiflexor muscles of young (12 wks age, N = 30) and old (30 mo age, N = 30) male Fischer 344 × Brown Norway rats were exposed to an acute protocol of 80 maximal SSCs (60 deg/s, 50 deg range of motion) in vivo using a custom-fabricated dynamometer. Performance was characterized by isometric performance, negative and positive work, and stretch-shortening parameters (peak eccentric force and minimum pre-stretch force) pre-exposure and at 6 hrs, 24 hrs, 48 hrs, 72 hrs, and 120 hrs after exposure (N= 6 young and 6 old animals at each time point). RESULTS: The isometric force, peak force, minimum force, negative work and positive work were not statistically different between groups before the exposure. However, after the SSC exposure, older age negatively affected the isometric performance (p = 0.0001), minimum force (p < 0.0001), peak eccentric force (p = 0.0002), negative work (p = 0.0005), and positive work (p < 0.0001). The isometric performance and dynamic performance (minimum force, peak force, negative work and positive work) differed most between the age groups 72 hours and 120 hours after the SSC exposure. At the 72 hour and 120 hour time points, the older group exhibited lower isometric force (p = 0.0125 and 0.0051, respectively), minimum force (p = 0.0149 and 0.0005, respectively), peak force (p = 0.0018 and 0.0239, respectively), negative work (p = 0.0050 and 0.0298, respectively), and positive work (p = 0.0190 and 0.0054, respectively) than their younger counterparts. CONCLUSIONS: Age negatively affected both the isometric and dynamic performance measures temporally after an acute exposure to SSCs, particularly at the later time points. These findings suggest that aging impairs the ability of skeletal muscle to adapt to an acute exposure of SSCs. Disclaimer: “The findings and conclusions in this report (abstract/presentation) have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy.”

Maximal Force Is Unaffected By Emphysema-Induced Atrophy In Extensor Digitorium Longus Muscle

Peripheral skeletal muscle function is altered in patients suffering from emphysema (EMP) and chronic obstructive pulmonary disease (COPD). Previously we have separately reported locomotory muscle atrophy and contractile dysfunction in hamsters with EMP. However, the consequence of EMP-induced atrophy on skeletal muscle function remains unappreciated. PURPOSE: To investigate the effect of EMP-induced atrophy on locomotory muscle force production. METHODS: Maximal force measures were determined in-vitro [stimulation current was amplified and supplied via square-wave pulses (200 μs duration), voltage and muscle length were adjusted to achieve maximum isometric force, and the muscle was stimulated at increasing frequencies (10-300 Hz) every minute until maximum isometric force (mN) was obtained] in extensor digitorium longus (EDL) muscles of male Syrian Golden Hamsters at 4 and 8 months following intratracheal instillation of either saline (CON=10/group) or elastase (25 units/100 g body weight, EMP=15/group). RESULTS: The presence of EMP (P<0.01) was verified visually and by measurement of excised lung volume (4-month: CON=1.6±0.3 g; EMP=4.0±1.2 and 8-month: CON=1.8±0.5 g; EMP=4.8±1.3). Four months following instillation, absolute EDL mass was similar between groups (CON=35.3+4, EMP=33.1+5, mg), but was significantly lower at 8 months (CON=36.4+9, EMP=30.9+5, mg (p=0.05)). There was no difference in EDL fiber cross-sectional area after 4-months (CON=669±200, EMP=742±147, um2) of EMP. However, EDL fiber atrophy occurred after 8-months of EMP (CON=604±98, EMP=495±136, μm2 (p<0.05)). Peak isometric force (absolute, relative to body mass, or relative to muscle mass) was not different between groups at either time point. However, peak force normalized for body mass increased as a function of increased relative lung volume (r=0.42; P<0.05). CONCLUSION: These findings support the notion that in the EDL EMP-induced skeletal muscle atrophy may not be reflected in maximal muscle force decrements reported in the patient population. Therefore, therapeutic interventions aimed at improving locomotory muscle force should be targeted accordingly.

MUSCLE PERFORMANCE CHARACTERISTICS OF HIP AND ANKLE EXTENSORS AND THEIR RELATIONSHIP TO GAIT IN PERSONS AFTER HIP FRACTURE.

Purpose/Hypothesis: Hip fracture adversely affects muscle performance and function. Muscle performance has been described as peak isometric force or isokinetic torque. However, the total force generated (impulse) during the initiation of contraction and the speed at which a person can generate the force (rate of force development (RFD)) may be as important as the peak values typically reported. The purpose of this report is to examine muscle performance characteristics (impulse, RFD, and peak torque) of the hip and ankle extensors and their relationship to walking speed, a measure of functional performance, in a sample of elders 6 months post hip fracture. Subjects: Twenty six patients (81 ± 6 yrs) who had completed all traditional, medicare-reimbursed rehabilitation were included in this study. They had an average of 4 comorbidities and were taking 5.5 medications. BMI was 27.4 ± 3.7 kg/m2. Materials/Methods: Measures included free and fast gait speed using the Gait Mat II; peak isometric torque; rate of force development; and impulse of the hip and ankle extensors using the Kincom and labview software. Results: Subjects produced significantly less isometric torque and did so more slowly on the involved side as compared to the non-fractured side. Comparing involved to uninvolved hip muscle performance characteristics, hip extensor impulse at 100 msec was 1.57 vs 1.83 N*m*sec and 4.44 vs 5.76 N*m*sec at 200 msec; hip extensor RFD at 100 msec was 199.1 vs 263.6 N*m*sec and 141.5 vs 200.7 N*m*sec at 200 msec; and hip extensor peak torque 62.5 vs 81.8 N*m. Comparing involved and uninvolved ankle muscle performance characteristics, ankle plantarflexion impulse at 100 msec was 0.96 vs 1.07 N*m*sec and 2.26 and 2.58 N*m*sec at 200 msec; ankle plantarflexion RFD at 100 msec was 62.8 vs 88.8 N*m/sec and 49.7 vs 63.6 N*m/sec at 200 msec; and ankle plantarflexion peak torque was 21.2 vs 24.3 N*m. Participants also walked more slowly in response to preferred (usual) speed (0.69 ± 0.18 m/sec) and fast speed commands (0.99 ± 0.27 m/sec) than age-matched peers. The relationships between muscle performance characteristics and gait speed were weak, at best(r values = 0.02–0.50). Conclusions: Muscle performance characteristics of the hip and ankle muscles have not been reported in persons after hip fracture. The results of this study suggest that the entire LE is impaired after traditional rehabilitation has stopped. Clinical Relevance: Exercise training may need to include rapid force production for the LE extensor muscle groups. It is not clear if gait speed is related to impulse or rate of force development in this small sample of elders post hip fracture.

Influences of ventilation on maximal isometric force of the finger flexors

Force production may be influenced by the phase of ventilation during which force is exerted. To examine the potential influences of ventilation on variability in maximal force measurements, we recorded peak isometric forces of the finger flexors during normal breathing, forced inspiration, forced expiration, and the Valsalva maneuver in 14 healthy adult subjects. The peak force increased significantly from forced inspiration to forced expiration (about 10%). Both forced expiration and inspiration resulted in increases in the flexor/extensor cocontraction ratio, whereas the Valsalva maneuver had no significant effects on maximal force or cocontraction ratio. Thus, this study clearly demonstrates the effects of ventilation on maximal finger force-generating capability. Ventilation needs to be controlled for accurate assessments of maximal force.

Effects of a Six-Week Eccentric Exercise Program on Patients with Patellar Tendinopathy: Single-Subject Research Study

Purpose: Eccentric exercise is commonly recommended in the conservative treatment of chronic tendinopathies. This single-subject research study evaluated the effects of a six-week eccentric exercise program developed for patients with patellar tendinopathy (jumper's knee). Methods: Four patients (mean age 23.75 years; three female, one male) with unilateral patellar tendinopathy participated in this study. A nonconcurrent multiple baseline design was implemented and involved repeated measures of knee pain, knee function, and peak isometric force of the quadriceps and hamstring muscles. Measurements of isokinetic average torque of the quadriceps and hamstring muscles were collected prebaseline and postintervention. The intervention phase involved a six-week eccentric exercise program. Data were analyzed both visually and statistically. Results: Visual results indicated reductions in intensity (n = 3) and unpleasantness (n = 3) of knee pain, improved knee function (n = 3), increased isometric quadriceps peak force of the ipsilateral side (n = 3) and the contralateral side (n = 4), increased isometric hamstring peak force of the ipsilateral side (n = 1) and the contralateral side (n = 1), and increased concentric average torque of the ipsilateral quadriceps (n = 2) and the contralateral side (n = 3). Most visual analyses were supported by the C-statistic. Discussion: The eccentric exercise program showed mixed clinical benefits for four patients with patellar tendinopathy. However, none of the patients achieved full recovery within the suggested six-week treatment period.