Relative Endurance of High- and Low-Strength Women

Abstract

The purpose of this study was to analyze the relative endurance ability of women in terms of muscle mass, static muscle strength, and critical occluding tension levels (COTL). Women physical education majors volunteered as subjects for this study (N = 56). The percentages of grip strength used for the relative endurance tests were 30%, 45%, 60%, and 75% with local circulation to the forearm muscles intact and artificially occluded by a pressure cuff. Analysis of the data revealed that there was no significant difference in the endurance times of high- and low-strength women. The relationship between grip strength and relative endurance time for each tension level was insignificant (r = ?.23 to ?.34). These findings were discussed in light of the relatively small differences in muscle mass and similarity in COTL of high- and low-strength women.     

Effect of Selected Doses of Alcohol on Fatigue Parameters of the Forearm Flexor Muscles

Abstract

The purpose of the present study was to enhance knowledge of the effect of alcohol on physical performance by analyzing the effect of a small and moderate dose of alcohol on several aspects of muscular strength and endurance; in addition to the standard dosages, a large dose was given to an experimental subgroup. The parameters studied included initial strength, maximal strength, steady state or final strength, total work, fatigable work and the rate of fatigue of the forearm flexors. Male university students (N = 35) served as subjects and underwent three trials of a standardized work task consisting of intermittent maximum contractions of the forearm flexors performed at the rate of 30/min. for 6 min. Prior to each trial, each subject consumed either a control, small, or moderate dose of alcohol. The statistical analysis indicated that a small or moderate dose of alcohol had no effect on five of the parameters under investigation. The mathematical analysis of the rate of fatigue indicated rather large differences between the main rate constants, but the findings must be interpreted cautiously due to the insignificant nature of the statistical analysis. It was concluded that a small or moderate amount of alcohol had no effect on the strength and endurance variables under investigation.     

A Cross-Sectional Study of Fitness Levels in a Movement Education Program (Bischoff & Lewis, 1987)

Abstract

The net speed of arm movement made in response to sounds of 45, 65 and 85 db. loudness was measured by chronoscope. Reaction time was excluded. Thirty-six college men were tested. In another experiment, the force of successive contractions of the forearm muscles in response to serial auditory stimuli spaced 5 sec. apart was measured by a recording dynamometer. In both experiments there was a balanced order of presenting the three stimulus intensities. In general, the louder sounds produced faster arm movements and stronger contractions of the muscles. In explanation, it is postulated that greater perceived stimulus intensity results in stronger excitation of the pyramidal tracts and consequently more forceful muscular contractions.     

Performing pull-ups with small climbing holds influences grip and biomechanical arm action

Pull-ups are often used by sport-climbers and other athletes to train their arm and back muscle capabilities. Sport-climbers use different types of holds to reinforce finger strength concomitantly. However, the effect of grip types on pull-up performance had not previously been investigated. A vertical force platform sensor measured the force exerted by climbers when performing pull-ups under six different grip conditions (gym-bar, large climbing hold, and four small climbing holds: 22mm, 18mm, 14mm, and 10mm). The electromyography of finger flexors and extensor muscles were recorded simultaneously. The maximal arm power and summed mechanical work were computed. The results revealed that the number of pull-ups, maximal power, and summed mechanical work decreased significantly with the size of the climbing hold used, even if no differences were found between a large climbing hold and a gym-bar. Electromyography of the forearm muscles revealed that the use of a climbing hold generated finger flexor fatigue and that the level of cocontraction was impacted by the different segment coordination strategies generated during the pull-ups. These findings are likely to be useful for quantifying training loads more accurately and designing training exercises and programs.     

Relationship of Individual Differences and Subsequent Changes in Static Strength with Speed of Forearm Flexion Movement

Abstract

This study investigated the relationship between strength and speed of forearm flexion and compared the effect of three methods of training on speed of forearm flexion movement. Ninety-one university freshmen were tested for maximum static strength, forearm mass, and speed of forearm flexion. They were assigned to four groups: control, speed of movement, isometric, and isotonic. After an 8-week experimental program, subjects were tested again for strength, mass, and speed of forearm flexion movement. Low positive relationships, significant at the .05 level, between static strength and speed of forearm flexion were found in this study. When static strength was related to the mass which was moved during movement, correlations between strength/mass and speed were not significant. The results of both correlational computations and covariance analysis indicated that increasing the strength of the muscles which move a limb does not result in a corresponding increase in the speed with which the limb can be moved.     

Factors affecting occlusion pressure and ischemic preconditioning

Purpose: To determine the effect of limb selection (upper/lower), cuff width (small (6?cm)/medium (13?cm) upper; medium/large (18?cm) lower) and anthropometry on arterial occlusion pressure (AOP) in ischemic preconditioning (IPC). Methods: Twenty athletes (10 females and 10 males) had surface anthropometry and dual x-ray absorptiometry (DXA) assessments before using Doppler ultrasound to confirm AOP for each limb. Subsequently, 5?min of occlusion occurred, with near-infrared spectroscopy (NIRS) measuring muscle oxygenation changes. Resultant AOP was compared between sexes, limbs and cuff sizes using linear regression models. Results: Mean AOP was higher in the lower limbs than the upper limbs (161?±?18 vs. 133?±?12?mm?Hg; p?p?p?=?.222). Sex and resting systolic blood pressure (SBP) accounted for 77% (small cuff) to 83% (medium cuff) of variance in AOP for upper limbs, and 61% (medium cuff) to 63% (large cuff) in lower limbs. Including anthropometry accounted for 82% (small cuff) to 89% (medium cuff) and 78% (medium cuff) to 79% (large cuff) of variance for upper and lower limbs, respectively. Adding DXA variables improved the explained variance up to 83% (small cuff) to 91% (medium cuff) and 79% (medium cuff) to 87% (large cuff) for upper and lower limbs, respectively. NIRS data showed significantly greater tissue oxygenation changes in upper versus lower limbs. Conclusions: The AOP in athletes is dependent on limb occluded, sex, SBP, limb and cuff size, and body composition.     

Intra-abdominal pressures during activity in women using an intra-vaginal pressure transducer

Abstract

Strenuous physical activity has been linked to pelvic floor disorders in women. Using a novel wireless intra-vaginal pressure transducer, intra-abdominal pressure was measured during diverse activities in a laboratory. Fifty-seven women performed a prescribed protocol using the intra-vaginal pressure transducer. We calculated maximal, area under the curve and first moment of the area intra-abdominal pressure for each activity. Planned comparisons of pressure were made between levels of walking and cycling and between activities with reported high pressure in the literature. Findings indicate variability in intra-abdominal pressure amongst individuals doing the same activity, especially in activities that required regulation of effort. There were statistically significant differences in maximal pressure between levels of walking, cycling and high pressure activities. Results for area under the curve and first moment of the area were not always consistent with maximal pressure. Coughing had the highest maximal pressure, but had lower area under the curve and first moment of the area compared to most activities. Our data reflect novel findings of maximal, area under the curve and first moment of the area measures of intra-abdominal pressure, which may have clinical relevance for how physical activity relates to pelvic floor dysfunction.     

Effect of bag holding on the center of foot pressure and the lower leg muscle activities

Abstract

This study examined the influence of holding a bag with one hand on the center of foot pressure (COP) and the electromyographic responses in lower leg muscles. Thirteen healthy male adults participated in this study to keep an upright posture while holding a load with the dominant hand with four bag weight conditions (0%, 15%, 30%, and 45% of maximal voluntary contraction (MVC) of the jerk strength). Integrated Electromyography (iEMG) and mean power frequency (MPF) of EMG were calculated to estimate the degree of muscle activity and fatigue in the tibialis anterior and soleus that are involved in ankle joint control. Body sway was evaluated by the mean position of left-right (X) and front-back (Y) axis sway and the following 4 body sway factors; unit time sway factor (F1), front-back sway factor (F2), left-right sway factor (F3), high frequency band power spectrum factor (F4). When holding a bag at 45% MVC or more of the jerk strength with a single hand for one minute, muscle activity in the lower leg on the side of the bag increased markedly, and muscle fatigue was induced in the antigravity muscles of both legs. As a result, anteroposterior sway increased to a short, quick sway.     

Reliability of EMG normalisation methods for upper-limb muscles

Abstract

The study investigated different electromyographic (EMG) normalisation methods for upper-limb muscles. This assessment aimed at comparing the EMG amplitude and the reliability of EMG values obtained with each method. Eighteen male tennis players completed isometric maximal voluntary contractions and dynamic strength exercises (push-ups and chin-ups) on three separate test sessions over at least 7 days. Surface EMG activity of nine upper body muscles was recorded. For each muscle, an analysis of variance for repeated measures was used to compare maximal EMG amplitudes between test conditions. The intra-class correlation coefficient, the coefficient of variation and the standard error of measurement were calculated to determine the EMG reliability of each condition. On the basis of a compromise between maximal EMG amplitude and high reliability, the chin-ups appeared to be the optimal normalisation method for M. latissimus dorsi, M. posterior deltoid, M. biceps brachii, M. flexor carpi radialis and M. extensor carpi radialis. The push-ups seemed relevant to normalise M. anterior deltoid and M. triceps brachii activity, while isometric maximal voluntary contraction remained the most appropriate method for M. pectoralis major and M. middle deltoid. Thus, original methods are proposed to normalise EMG signal of upper-limb muscles.     

Examining the intrinsic foot muscles’ capacity to modulate plantar flexor gearing and ankle joint contributions to propulsion in vertical jumping

BackgroundDuring human locomotion, a sufficiently stiff foot allows the ankle plantar flexors to generate large propulsive powers. Increasing foot stiffness (e.g., via a carbon plate) increases the ankle's external moment arm in relation to the internal moment arm (i.e., increasing gear ratio), reduces plantar flexor muscles’ shortening velocity, and enhances muscle force production. In contrast, when activation of the foot's intrinsic muscles is impaired, there is a reduction in foot and ankle work and metatarsophalangeal joint stiffness. We speculated that the reduced capacity to actively control metatarsophalangeal joint stiffness may impair the gearing function of the foot at the ankle.MethodsWe used a tibial nerve block to examine the direct effects of the intrinsic foot muscles on ankle joint kinetics, in vivo medial gastrocnemius’ musculotendinous dynamics, and ankle gear ratio on 14 participants during maximal vertical jumping.ResultsUnder the nerve block, the internal ankle plantar flexion moment decreased (p = 0.004) alongside a reduction in external moment arm length (p = 0.021) and ankle joint gear ratio (p = 0.049) when compared to the non-blocked condition. Although medial gastrocnemius muscle–tendon unit and fascicle velocity were not different between conditions, the Achilles tendon was shorter during propulsion in the nerve block condition (p < 0.001).ConclusionIn addition to their known role of regulating the energetic function of the foot, our data indicate that the intrinsic foot muscles also act to optimize ankle joint torque production and leverage during the propulsion phase of vertical jumping.     

Can changes in midsole bending stiffness of shoes affect the onset of joint work redistribution during a prolonged run?

Purpose:This study aimed to investigate if changing the midsole bending stiffness of athletic footwear can affect the onset of lower limb joint work redistribution during a prolonged run.Methods:Fifteen trained male runners(10-km time of <44 min) performed 10-km runs at 90% of their individual speed at lactate threshold(i.e.,when change in lactate exceeded 1 mmol/L during an incremental running test) in a control and stiff shoe condition on 2 occasions.Lower limb joint kinematics and kinetics...     

Cardiovascular Responses to Sustained Isometric Work in a Hot Environment

The purpose of this study was to investigate the alterations in blood pressure, heart rate (HR), left ventricular ejection time (LVET), and myocardial oxygen consumption (as depicted by TRIP) during a maximal and submaximal isometric contraction of the forearm in a closed heated environment. Simultaneous recordings of the ECG, carotid pulse wave, blood pressure, and skin temperature were taken from a sitting position during rest and static exertion. Twelve male subjects 20 to 31 years old (mean age = 25.4) were tested in room temperature and in a closed sauna where skin temperature was maintained between 40°C and 41 °C. Analysis of variance demonstrated that although the oxygen consumption of the myocardium (TRIP index) increased (p < .001) during isometric handgrip contraction, there was no appreciable change when heat stress was introduced. Although systolic (BPs) and diastolic (BPd) arterial pressures rose (p < .001) during static exertion they were substantially lower (p < .001) when forearm contraction was performed under heat stress. As HR increased LVET was reduced (p < .001) during static exertion. Body heating produced a further increase (p = .001) in HR and subsequent reduction (p = .001) in LVET. Of novel interest is the finding that alterations in blood pressure and the triple index produced by isometric work are partially masked by opposite responses associated with thermoregulation. In contrast changes in HR and LVET caused by isometric exertion are completely additive to those associated with thermoregulation.     

Forearm oxygenation and blood flow kinetics during a sustained contraction in multiple ability groups of rock climbers

Currently, the physiological mechanisms that allow elite level climbers to maintain intense isometric contractions for prolonged periods of time are unknown. Furthermore, it is unclear whether blood flow or muscle oxidative capacity best governs performance. This study aimed to determine the haemodynamic kinetics of 2 forearm flexor muscles in 3 ability groups of rock climbers. Thirty-eight male participants performed a sustained contraction at 40% of maximal voluntary contraction (MVC) until volitional fatigue. Oxygen saturation and blood flow was assessed using near infrared spectroscopy and Doppler ultrasound. Compared to control, intermediate, and advanced groups, the elite climbers had a significantly (P < 0.05) higher strength-to-weight ratio (MVC/N), de-oxygenated the flexor digitorum profundus significantly (P < 0.05) more (32, 34.3, and 42.8 vs. 63% O₂, respectively), and at a greater rate (0.32, 0.27, and 0.34 vs. 0.77 O₂%·s^?1, respectively). Furthermore, elite climbers de-oxygenated the flexor carpi radialis significantly (P < 0.05) more and at a greater rate than the intermediate group (36.5 vs. 14.6% O₂ and 0.43 vs. 0.1O₂%·s^?1, respectively). However, there were no significant differences in total forearm ? blood flow. An increased MVC/N is not associated with greater blood flow occlusion in elite climbers; therefore, oxidative capacity may be more important for governing performance.     

Biomechanical factors affecting energy cost during running utilising different slopes

ABSTRACT

This study aimed to examine the characteristics of electromyography (EMG) and kinematics of the supporting leg affecting energy cost while running at incline, level, and decline slopes. Twelve male Japanese middle- and long-distance runners volunteered for this study. The subjects were asked to run at 13.5 km·h^?1 on a treadmill under three slope conditions. Sagittal plane kinematics and the EMG of the lower limb muscles, respiratory gases were recorded. Energy cost differed significantly between slopes, being the lowest in decline slope and the greatest in incline slope. Integrated EMG (iEMG) of leg extensor muscles was greater in the incline slope than in the decline slope, and iEMG of the gastrocnemius and soleus muscles correlated positively with energy cost. The knee and ankle joint kinematics were associated with energy cost during running. In incline slope, the knee and ankle joints were more extended (plantarflexed) to lift the body. These movements may disturb the coordination between the ankle and knee joints. The gastrocnemius muscle would do greater mechanical work to plantarflex the ankle joint rather than transfer mechanical energy as well as greater mechanical work of mono-articular muscles. These muscular activities would increase energy cost.     

Comparison of twitch contractile properties of plantarflexor muscles in Nordic combined athletes,cross-country skiers,and sedentary men

Abstract

The purpose of this study was to compare twitch contractile properties of skeletal muscles in male athletes who train for power and endurance simultaneously (Nordic combined athletes) with athletes who train for endurance (cross-country skiers) and sedentary individuals. Ten Nordic combined athletes, 13 cross-country skiers, and 14 sedentary males aged 20–26 years participated. To determine the contractile properties of the plantarflexor muscles during isometric twitch, the posterior tibial nerve in the popliteal fossa was stimulated by supramaximal square wave pulses of 1 ms duration. Twitch peak force, maximal rates of force development and relaxation, contraction and half-relaxation times were measured. The percentage increase in twitch peak force after a 5-s maximal voluntary contraction (MVC) was taken as an indicator of post-activation potentiation. Nordic combined athletes had a significantly greater twitch post-activation potentiation and rate of force development and shorter contraction time than the other two groups (P < 0.05). They also had a greater (P < 0.05) twitch peak force than cross-country skiers. No significant differences in measured twitch contraction characteristics were found in cross-country skiers and sedentary males. We conclude that the twitch contractile properties of the plantarflexor muscles differed markedly in athletes who train for power and endurance simultaneously compared with athletes who predominantly train for endurance. As an indicator of long-term adaptation to simultaneous power and endurance training, increased twitch force-generation and potentiation capacity, and shortening of twitch contraction times in the plantarflexor muscles were observed in Nordic combined athletes.     

Gender,age, and sport differences in relative age effects among US Masters swimming and track and field athletes

Abstract

The aim of the present study was to examine elbow joint extension power-load characteristics with and without a countermovement. Eight male participants performed maximal elbow extensions with and without a countermovement against different loads (0, 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 kg). Electromyographic activity of the lateral and long heads of the triceps brachii and the biceps brachii muscles was recorded. The average joint power in the concentric phase was significantly enhanced in the countermovement condition at all loads except for 0 kg. The optimal load for the maximal joint power was greater in the countermovement (7.5 kg) than in the no countermovement condition (5.0 kg). Electromyographic activity was unchanged over the intensities and conditions. Our results suggest that the optimal load for the maximal joint power depends on the type of action (i.e. with or without a counter-movement), and that the enhanced joint power in the countermovement condition is due primarily to the storage and utilization of elastic energy.     

Muscular Fatigue Curves of Boys and Girls

Abstract

Exponential fatigue curves for dynamic work of the forearm muscles were obtained from 200 boys arid girls ranging from 8 through 17 years of age. The fatigue parameters analyzed in relation to initial strength were fatigable strength, steady-state equilibrium strength, and relative rate of strength loss per contraction. Older children were stronger and exhibited greater fatigue. When their strength loss and steady-state levels were considered in relation to their initial strength-capacity, there were no age differences in fatigability, and sex differences were either absent or very small. At age eight, boys and girls had equal rates of strength loss per muscle contraction. Older boys, since they exerted more strength initially, tended to reach the fatigue level more rapidly than younger children. Older girls reached their fatigue level more slowly.     

The effects of maximal and submaximal arm crank ergometry and cycle ergometry on postural sway

Abstract

This study aimed to determine whether arm crank ergometry (ACE) disturbed postural sway to the same extent as cycle ergometry (CE). Nine healthy, none specifically trained adults undertook posturographic tests before and after five separate exercise trials consisting of: two incremental exercise tests to exhaustion for ACE and CE to examine postural sway responses to maximal exercise and to determine peak power output (W_max); two subsequent tests of 30 min duration for ACE and CE at a relative workload corresponding to 50% of the ergometer-specific W_max (ACE_rel; 53 ± 8 W and CE_rel; 109 ± 16 W). A final CE trial was performed at the same absolute power output (CE_abs) as the submaximal ACE trial to match absolute exercise intensity (i.e., 53 ± 8 W). The centre of pressure (COP) displacement was recorded using a force platform before, immediately after exercise and during a 30-min recovery period. ACE had no effects on postural sway (P > 0.05). An increase in mediolateral COP displacement was observed following maximal CE only (P = 0.001), while anteroposterior COP displacement and COP path length increased following maximal and submaximal CE (P < 0.05). These differences in postural sway according to exercise mode likely stem from the activity of postural muscles when considering that CE recruits lower limb muscles involved in balance. This study provides evidence of an exercise mode which does not elicit post-exercise balance impairments, therefore possesses applications to those at an increased risk of falling.     

Evolution of muscular fatigue in periscapular and rotator cuff muscles during isokinetic shoulder rotations

To this day, how shoulder muscles react to a strong fatigue stimulus during dynamic shoulder rotations remains unknown. The aims of this study were to assess the effect of repeated maximal internal-external isokinetic shoulder rotations on shoulder strength and muscle activity. Twenty-four individuals completed a 50-repetition fatiguing isokinetic protocol while electromyography was recorded on eleven muscles of the shoulder girdle. Time-frequency transformation and an ANOVA model using statistical parametric mapping methods were used to analyze shifts in instantaneous median frequency (MDF) between each 10-repetition Blocks. Peak torques decreased in both internal and external rotation (P < 0.01) by 24.8% on average which indicated the presence of fatigue. Significant decrease in MDF (P < 0.01) was observed for pectoralis, middle deltoid, upper, middle and lower trapezius, infraspinatus and subscapularis muscles. The observed fatigue to the periscapular and rotator cuff muscles suggests that shoulder stability could be compromised during repeated shoulder rotations, which could underlie the increased risk of scapular dyskinesis and shoulder impingement during fatiguing tasks. The present study provides a deeper understanding on the manifestations of fatigue within muscles of the shoulder girdle and the results could be applied toward improvements in athlete shoulder injury prevention and rehabilitation programs.     

Grip and Forearm Position Effects on Tests of Static and Dynamic Upper Body Endurance

Abstract

The effects of grip and forearm position on two tests of upper body muscular endurance were investigated in 109 male subjects 18–21 years of age. Subjects were systematically presented 12 tasks: six pull-up and six straight-arm hang grip and forearm variations. Each of the six tasks for both endurance tests represented a different combination of grip (thumb over bar and thumb under bar) and forearm position (pronated, supinated and semi-pronated). Task results were analyzed utilizing 2 × 3 (grip × forearm) ANOVA with repeated measures on the two factors. Analysis of pull-up data revealed that the semi-pronated and supinated forearm positions were not statistically different from each other, but superior to the pronated condition. Results of straight-arm hang performance revealed a significant difference between grips at the semi-pronated position, with the “thumb under bar” being superior. Results for forearm positions at grips indicated a significant difference for the “thumb under bar,” with the pronated and semi-pronated positions being superior to the supinated position. For forearm positions at “thumb over bar,” the pronated condition was significantly different from the semi-pronated and supinated positions. Thumb position trends and kinesiological mechanical analysis did foster general recommendations for use of the “thumb over bar” for pull-ups and the “thumb under bar” position for the straight-arm hang.