Characteristics of the Achilles Tendon Reflex Following Isometric and Isotonic Exercise

Abstract

An investigation was conducted to determine the effects of fatiguing exercise upon the Achilles tendon reflex. Eleven subjects performed one of four exercise tasks on each of four separate days. The exercise conditions involved low-intensity isometric, high-intensity isometric, low-intensity isotonic or high-intensity isotonic exercise. The low-intensity tasks required a 25% MVC load, while the high-intensity conditions required a 50% MVC load. Results showed that low-intensity isometric exercise reduced reflex force, as well as the time needed to reach peak force, while high-intensity exercise produced an enhancement of reflex force. Half-relaxation time was faster after subjects executed low-intensity isometric exercise, but generally somewhat prolonged following high-intensity isometric exercise. Thus, the Achilles tendon reflex may be either enhanced or depressed depending upon the type and intensity of exercise performed.     

The acute effects of bodyweight suspension exercise on muscle activation and muscular fatigue

This investigation examined effects of two exercise modes (barbell, BB; bodyweight suspension, BWS) on muscle activation, resistance load, and fatigue. During session one, nine resistance-trained males completed an elbow flexion one-repetition maximum (1RM). During sessions two and three, subjects completed standing biceps curls to fatigue at 70% 1RM utilizing a randomized exercise mode. Surface electromyography (sEMG) recorded muscle activation of the biceps brachii, triceps brachii, anterior deltoid, posterior deltoid, rectus abdominis, and erector spinae. BWS resistance load was measured using a force transducer. Standing maximal voluntary isometric contractions of the elbow flexors recorded at 90° were used to determine the isometric force decrement and rate of fatigue (ROF) during exercise. sEMG and resistance load data were divided into 25% contraction duration bins throughout the concentric phase. BWS resulted in a 67.7?±?7.4% decline in resistance load throughout the concentric phase (p?≤?0.05). As a result, BB elicited higher mean resistance loads (31.4?±?4.0?kg) and biceps brachii sEMG (84.7?±?27.8% maximal voluntary isometric contractions, MVIC) compared with BWS (20.4?±?3.4?kg, 63.4?±?21.6% MVIC). No difference in rectus abdominis or erector spinae sEMG was detected between exercise modes. Isometric force decrement was greater during BWS (?21.7?±?7.0?kg) compared with BB (?14.9?±?4.7?kg); however, BB (?3.0?±?0.8?kg/set) resulted in a steeper decline in ROF compared with BWS (?1.7?±?0.6?kg/set). The variable resistance loading and greater isometric force decrement observed suggest that select BWS exercises may resemble variable resistance exercise more than previously considered.     

The relationships between exercise intensity, heart rate, and blood pressure during an incremental isometric exercise test

Currently, it is not possible to prescribe isometric exercise at an intensity that corresponds to given heart rates or systolic blood pressures. This might be useful in optimizing the effects of isometric exercise training. Therefore, the aim of this study was to explore the relationships between isometric exercise intensity and both heart rate and systolic blood pressure during repeated incremental isometric exercise tests. Fifteen participants performed seated isometric double-leg knee extension, during which maximum voluntary contraction (MVC) was assessed, using an isokinetic dynamometer. From this, a corresponding peak electromyographic activity (EMG(peak)) was determined. Subsequently, participants performed two incremental isometric exercise tests (at least 48 h apart) at 10, 15, 20, 25, and 30% EMG(peak), during which steady-state heart rate and systolic blood pressure were recorded. In all participants, there were linear relationships between %EMG(peak) and heart rate (r at least 0.91; P < 0.05) and between %EMG(peak) and systolic blood pressure (r at least 0.92; P < 0.05). Also, when repeated tests were compared, there were no differences in the slopes (P > 0.50) or elevations (P > 0.10) for either of the relationships. Therefore, these linear relationships could be used to identify isometric exercise training intensities that correspond to precise heart rates or systolic blood pressures. Training performed in this way might provide greater insight into the underlying mechanisms for the cardiovascular adaptations that are known to occur as a result.     

划船运动员静力及动力性肌肉运动疲劳时肌氧含量的变化特征及对EMG参数的影响

研究目的：1）研究静力和动力性肌肉运动疲劳时肌肉氧含量的变化特点厦其规律；2）了解静力性、动力性递增强度运动时EMG参数变化；3）探讨肌氧含量与EMG参数变化之间的关系，为肌肉疲劳时影响肌电肌氧机制提供可能的理论基础。研究方法：1）肌氧含量的测试：探头纵向旋转让光源和检测器的轴线平行于股外侧肌外侧头大腿测定运动时肌氧含量的变化；2）肌电的测试：采用表面肌电图的测量，得出表面电图各指标参数；3）静力负荷等长收缩：通过力量传感器测出其最大肌肉收缩所对应的MVC；4）动力性负荷运动：采取功率自行车逐级递增负荷的测试方法作为肌肉的动力性运动，同步记录EMG参数，并在每一级负荷朱30S采血测定血乳酸浓度。结论：静力性运动时E／T值大幅度增大的时间大多出现在肌氧停止下降之后，肌氧的降低程度与肌肉疲劳程度有关。动力性运动时血乳酸值随负荷而增加，IEMG的变化趋势与血乳酸相似，IEMG、Oxy-Hb、BI值三者呈非常显著性相关，表明肌肉疲劳时肌肉氧供和内环境的改变也是影响EMG信号的重要因素。     

Acute intraocular pressure changes during isometric exercise and recovery: The influence of exercise type and intensity,and participant´s sex

ABSTRACT

We assessed the intraocular pressure (IOP) behaviour during a 1-minute period of isometric physical effort and the immediate 1-minute of recovery in the mid-thigh clean pull and squat exercises at three different intensities. Twenty physically active individuals performed the isometric mid-thigh clean pull and squat exercises at three intensities (0% [low-intensity], 25% [medium-intensity] and 50% [high-intensity] of the maximum isometric force). IOP was semi-continuously measured by rebound tonometry. There was a statistically significant effect of exercise intensity on IOP (p < 0.001, ?_p² = 0.416), observing that IOP increments were positively associated with exercise intensity. The mid-thigh clean pull and squat exercises did not demonstrate differences (p = 0.510), and also, no differences were observed between men and women (p = 0.683). The IOP changes during the isometric physical effort showed a positive linear behaviour in all conditions (r = 0.70 to 0.96). IOP returned to baseline levels after 8 seconds of recovery. Our data showed a progressive and instantaneous IOP increment during isometric exercise, which was positively associated with exercise intensity. IOP changes were independent on the type of exercise and participant´s sex. After exercise, IOP rapidly (≈ 8 seconds) returned to baseline levels.     

Muscle Fiber Type Composition and Knee Extension Isometric Strength Fatigue Patterns in Power- and Endurance-Trained Males

Abstract

Muscle fiber type composition in the vastus lateralis and knee extension isometric strength fatigue patterns were assessed in eight endurance-trained and eight power-trained males. Two different 25-trial isometric contraction exercise regimens were administered: a 10-second contraction, 5-second intertrial rest condition designed to induce a fast rate of fatigue and a 10-second contraction, 20-second intertrial rest condition designed to induce a slower rate of fatigue. The power group fatigued almost four times faster than the endurance group in the 10:5 exercise condition. In the 10:20 exercise condition, the endurance group showed no fatigue pattern while the power group had a significant strength decrement of 32%. In both exercise conditions, the power group exhibited more complex fatigue patterns in terms of statistically significant trend components. Maximum isometric strength correlated positively with slow twitch (ST) percent number in power (r = .80) and endurance (r = .48) groups, but negatively with linear trend coefficients in endurance (r = -.62) and power (r = -.80) groups. Maximum isometric strength also correlated higher with fatigue curve trend coefficients than did muscle fiber type composition. Thus, a faster rate of fatigue was associated with higher maximum isometric strength and with higher ST percent number and area. Since maximum isometric strength correlated with body weight (r = .86 for groups combined), both maximum isometric strength and muscle mass appear to be more important determinants of knee extension isometric strength fatigue patterns than muscle fiber type composition.     

运动员心脏与超声心动技术

运动员心脏是心脏对不同形式运动负荷在不同时期产生的适应性的改变。已有的研究提示，一般认为等张运动导致心腔扩大，等长运动导致心肌肥厚，但在实际训练中，并不存在单纯的等张或等长训练。运动员心脏增大的原因有可能是血流动力学过载、遗传因素及内分泌因素等多方面的影响。超声心动技术由于方法简单准确和无创，是评定运动员心脏功能与运动员选材的重要手段。     

Influence of bench angle on upper extremity muscular activation during bench press exercise

This study compared the muscular activation of the pectoralis major, anterior deltoid and triceps brachii during a free-weight barbell bench press performed at 0°, 30°, 45° and –15° bench angles. Fourteen healthy resistance trained males (age 21.4 ± 0.4 years) participated in this study. One set of six repetitions for each bench press conditions at 65% one repetition maximum were performed. Surface electromyography (sEMG) was utilised to examine the muscular activation of the selected muscles during the eccentric and concentric phases. In addition, each phase was subdivided into 25% contraction durations, resulting in four separate time points for comparison between bench conditions. The sEMG of upper pectoralis displayed no difference during any of the bench conditions when examining the complete concentric contraction, however differences during 26–50% contraction duration were found for both the 30° [122.5 ± 10.1% maximal voluntary isometric contraction (MVIC)] and 45° (124 ± 9.1% MVIC) bench condition, resulting in greater sEMG compared to horizontal (98.2 ± 5.4% MVIC) and –15 (96.1 ± 5.5% MVIC). The sEMG of lower pectoralis was greater during –15° (100.4 ± 5.7% MVIC), 30° (86.6 ± 4.8% MVIC) and horizontal (100.1 ± 5.2% MVIC) bench conditions compared to the 45° (71.9 ± 4.5% MVIC) for the whole concentric contraction. The results of this study support the use of a horizontal bench to achieve muscular activation of both the upper and lower heads of the pectoralis. However, a bench incline angle of 30° or 45° resulted in greater muscular activation during certain time points, suggesting that it is important to consider how muscular activation is affected at various time points when selecting bench press exercises.     

不同形式肌肉收缩时肌电参数变化特征及机制

研究目的：探讨动力性与静力性肌肉收缩时EMG各参数的变化特征及疲劳时各指标的差异，比较不同项目运动员肌肉收缩特征对EMG参数的影响及与该项目的关系。研究方法：27名受试者分为两组，第一组为赛艇运动员（组一），第二组为田径爆发性力量项目（跳跃、短跑）专选运动员（组二）。受试者以2／3Mvc做静力性持续等长收缩，动力性持续肌肉收缩则采用本人的MVC，同时记录EMG信号，分析IEMG、E／T值和MF。研究结果：持续静力性肌肉收缩时，随疲劳的发展赛艇运动员与田径运动员IEMG、E／T值均显著升高。但赛艇运动员从运动开始至80％时段一直保持平稳，此后迅速上升。静力性收缩时两组运动员随疲劳发展MF从高频向低频转移，但田径运动员频率下降速率要快于赛艇运动员。结论：赛艇运动训练促使大脑皮层动员运动单位工作更具有时间耐久性。快速、爆发式运动使疲劳时大脑皮层兴奋性下降更快，肌肉更易于疲劳。     

Effect of Unilateral Isometric and Isotonic Contractions on the Strength of the Contralateral Limb

Abstract

Two groups of college men (N = 41) participated for 12 weeks in two different exercise programs to determine the relative effects of unilateral isometric and isotonic contractions of equal load, duration, and range of movement on the muscular strength of the contralateral limb. Data examined by the t test for correlated means indicated that both methods of exercise produced significant increases in the strength of the unexercised limb. Application of the multiple linear regression technique for covariance analysis revealed that no significant difference existed between the effectiveness of the exercise methods.     

The Effect of Depth Jumps and Weight Training on Leg Strength and Vertical Jump

Abstract

In recent years, a method of plyometrics (exercises that cause a rapid lengthening of a muscle prior to contraction) called depth jumping has become a part of the training routine of many athletes. Two experiments are described in which the effectiveness of the exercises is examined. In Experiment 1, undergraduate students in beginning weight training classes trained with three different jumping programs: (1) maximum vertical jumps, (2) 0.3 m depth jumps, and (3) 0.75 m and 1.10 m depth jumps. In addition, all groups also lifted weights. In Experiment 2, a weight training class and the volleyball team at Brigham Young University-Hawaii were divided into two groups. One group lifted weights and performed 0.75 and 1.10 m depth jumps. The other group only lifted weights. In Experiment 1, the three training programs resulted in increases in one repetition maximum (1 RM) squat strength, isometric knee extension strength, and in vertical jump; however, there were no significant differences between treatments. In Experiment 2, all groups made significant increases in vertical jump, except the group of weight lifters, who did no jumping. It was concluded that depth jumps are effective but not more effective than a regular jumping routine.     

Leisure Attitudes of Varsity Athletes vs. NonVarsity Athletes

Abstract

Students (N = 104) enrolled in four low fitness, one middle fitness, and one high fitness class in basic physical education classes at the University of Connecticut participated in a 4-week program of isometric exercises done with an adjustable nylon belt which was stabilized against various body segments. Low, middle, and high fitness classes were compared in the amount of improvement made in the 5 items in which significant gains had been made. The MWF classes which did 30 min. of isometric exercises for 12 class meetings were compared to the TTh classes which met for 8 class meetings and which did the same isometric exercise program and in addition did stretching exercises and ran a mile.

When all groups were treated together, mean gains of 1.1 in. in the vertical jump, .74 sec. in the agility run, .17 sec. in the 30-yd. dash, 151.9 lb. in the leg lift, and 57.0 lb. in the back lift were made. These were all significant at the 0.005 to the 0.0005 level. Small but significant gains were made in right and left grip, the Fait endurance hang, and the 380-yd. run. The low fitness classes made greater improvements in the leg lift, the vertical jump, and the agility run than did the middle or high fitness groups. The high fitness class made greater improvements in the back lift and in the 30-yd. dash than did the low or middle fitness classes. The classes which did only isometric exercises for a half-hour three times each week for 4½ weeks made greater mean gains in the vertical jump, the agility run, the 30-yd. dash and the back lift than did the classes which met for 60-min. periods twice each week for 4½ weeks and did stretching exercises and running in addition to the isometric exercises. However, the latter made greater gains in the leg lift.     

A novel method for the performance of isometric exercise in the home

There is a paucity of research on devices suitable for home-based isometric exercise. Our aim was to compare cardiovascular responses to isometric exercise using novel and established methods. Ten individuals (age 34.0 +/- 8.5 years, mass 68.2 +/- 10.4 kg, height 1.72 +/- 0.09 m; mean +/- s) performed three different isometric exercise protocols with 48 h between each. Each protocol involved four repeated exercise bouts of 2 min at 30% maximum voluntary contraction force using alternate legs (transducer), alternate arms (transducer), or alternate arms (novel device). Systolic blood pressure, diastolic blood pressure, mean arterial blood pressure and heart rate were measured every 30 s. The highest (peak) values during each 2 min bout of exercise were recorded (peak systolic blood pressure, peak diastolic blood pressure, peak mean arterial blood pressure and peak heart rate). At the end of each 2 min exercise bout, the participants rated their perceived discomfort using Borg's CR-10 scale. There was a statistically significant difference in peak systolic blood pressure between isometric arm flexion using the force transducer and the novel device [158.1 +/- 10.8 vs. 149.1 +/- 13.9 mmHg (mean +/- s); P = 0.02]. Further analysis showed that peak systolic blood pressure was on average 9 mmHg higher using the force transducer with limits of agreement of - 15.97 to 33.97 mmHg. Analysis of the peak diastolic blood pressure, peak mean arterial blood pressure, peak heart rate and CR-10 data revealed no statistically significant differences between the three protocols. These results suggest that this novel, home-based method elicited similar cardiovascular responses during isometric exercise to those of established laboratory-based methods. However, the lower peak systolic blood pressure using the modified scales warrants further investigation before this method is used widely in the home.     

Isometric exercise and cognitive function: an investigation of acute dose–response effects during submaximal fatiguing contractions

The purpose of this study was to explore the dose–response relationship between exercise and cognitive performance using an acute bout of isometric exercise. University students (N = 55) were randomly assigned to control, 30%, 50% and 70% of maximum voluntary handgrip contraction groups. Participants performed a modified Stroop task before and after completion of an isometric handgrip endurance trial at their assigned exercise intensity. Ratings of perceived exertion (RPE) and forearm muscle activation (EMG) showed linear trends of progressively greater RPE and muscle activation at greater exercise intensity levels. Regression analysis showed significant (P < .05) linear degradations in frequency of errors on the Stroop task with increasing exercise intensity. We conclude that performing isometric exercise until exhaustion is associated with reduced cognitive performance and that higher intensity isometric exercise leads to greater performance impairments in a linear dose–response manner.     

Eccentric exercise-induced muscle weakness abolishes sex differences in fatigability during sustained submaximal isometric contractions

BackgroundFemales are typically less fatigable than males during sustained isometric contractions at lower isometric contraction intensities. This sex difference in fatigability becomes more variable during higher intensity isometric and dynamic contractions. While less fatiguing than isometric or concentric contractions, eccentric contractions induce greater and longer lasting impairments in force production. However, it is not clear how muscle weakness influences fatigability in males and females during sustained isometric contractions.MethodsWe investigated the effects of eccentric exercise-induced muscle weakness on time to task failure (TTF) during a sustained submaximal isometric contraction in young (18–30 years) healthy males (n = 9) and females (n = 10). Participants performed a sustained isometric contraction of the dorsiflexors at 35° plantar flexion by matching a 30% maximal voluntary contraction (MVC) torque target until task failure (i.e., falling below 5% of their target torque for ≥2 s). The same sustained isometric contraction was repeated 30 min after 150 maximal eccentric contractions. Agonist and antagonist activation were assessed using surface electromyography over the tibialis anterior and soleus muscles, respectively.ResultsMales were ∼41% stronger than females. Following eccentric exercise both males and females experienced an ∼20% decline in maximal voluntary contraction torque. TTF was ∼34% longer in females than males prior to eccentric exercise-induced muscle weakness. However, following eccentric exercise-induced muscle weakness, this sex-related difference was abolished, with both groups having an ∼45% shorter TTF. Notably, there was ∼100% greater antagonist activation in the female group during the sustained isometric contraction following exercise-induced weakness as compared to the males.ConclusionThis increase in antagonist activation disadvantaged females by decreasing their TTF, resulting in a blunting of their typical fatigability advantage over males.     

A novel method for the performance of isometric exercise in the home

There is a paucity of research on devices suitable for home-based isometric exercise. Our aim was to compare cardiovascular responses to isometric exercise using novel and established methods. Ten individuals (age 34.0?±?8.5 years, mass 68.2?±?10.4?kg, height 1.72?±?0.09?m; mean?±?s) performed three different isometric exercise protocols with 48?h between each. Each protocol involved four repeated exercise bouts of 2?min at 30% maximum voluntary contraction force using alternate legs (transducer), alternate arms (transducer), or alternate arms (novel device). Systolic blood pressure, diastolic blood pressure, mean arterial blood pressure and heart rate were measured every 30?s. The highest (peak) values during each 2?min bout of exercise were recorded (peak systolic blood pressure, peak diastolic blood pressure, peak mean arterial blood pressure and peak heart rate). At the end of each 2?min exercise bout, the participants rated their perceived discomfort using Borg's CR-10 scale. There was a statistically significant difference in peak systolic blood pressure between isometric arm flexion using the force transducer and the novel device [158.1?±?10.8 vs. 149.1?±?13.9?mmHg (mean?±?s); P = 0.02]. Further analysis showed that peak systolic blood pressure was on average 9?mmHg higher using the force transducer with limits of agreement of –?15.97 to 33.97?mmHg. Analysis of the peak diastolic blood pressure, peak mean arterial blood pressure, peak heart rate and CR-10 data revealed no statistically significant differences between the three protocols. These results suggest that this novel, home-based method elicited similar cardiovascular responses during isometric exercise to those of established laboratory-based methods. However, the lower peak systolic blood pressure using the modified scales warrants further investigation before this method is used widely in the home.     

Effect of Isometric and Isotonic Exercise Programs upon Muscular Endurance

Abstract

Three groups of 11 subjects enrolled in required physical education were equated on the basis of bicycling for two minutes at 14 kg. resistance. Group I did weight training, Group II used the Commander Set series of isometric contractions, and Group III participated in normal activities. At the conclusion of the 8-week experimental period all subjects were retested on the bicycle ergometer under the original conditions. Both experimental groups showed statistically significant improvements in the bicycle ergometer test and there were no statistically significant differences between the means of the differences between the initial and final scores of the two experimental groups. It is hypothesized that increases in muscular endurance may be effected by certain programs of isometric contractions as well as by isotonic exercises.     

Acute effects of aerobic exercise performed with different volumes on strength performance and neuromuscular parameters

The aim of the present study was to investigate the acute effect of the aerobic exercise volume on maximum strength and strength-endurance performance; and possible causes of strength decrements (i.e. central and peripheral fatigue). Twenty-one moderately trained men were submitted to a maximal incremental test to determine anaerobic threshold (AnT) and maximum dynamic strength (1RM) and strength-endurance (i.e. total volume load [TV]) tests to determine their baseline strength performance. Following, subjects performed six experimental sessions: aerobic exercise sessions (continuous running at 90% AnT) with different volumes (3?km, 5?km or 7?km) followed by 1RM or strength-endurance test in the 45° leg press exercise. Maximum voluntary isometric contraction (MVIC), voluntary activation (VA) level, contractile properties, and electromyographic activity (root mean square [RMS]) of the knee extensor muscles were assessed before and after aerobic exercises and after strength tests. TV was lower after 5?km and 7?km runs than in the control condition (12% and 22%, respectively). Additionally, TV was lower after 7?km than 3?km (14%) and 5?km (12%) runs. MVIC, VA, RMS, and contractile properties were reduced after all aerobic exercise volumes (～8%, ～5%, ～11% and ～6–14%, respectively). Additionally, MVIC, VA, and contractile properties were lower after strength tests (～15%, ～6%, ～9–26%, respectively). In conclusion, strength-endurance performance is impaired when performed after aerobic exercise and the magnitude of this interference is dependent on the aerobic exercise volume; and peripheral and central fatigue indices could not explain the different TV observed.     

Changes in leg strength 8 and 32 h after endurance exercise

The aim of this study was to determine the effects of a single bout of endurance exercise on subsequent strength performance. Eight males with a long history of resistance training performed isokinetic, isometric and isotonic leg extension strength tests 8 and 32 h after 50 min of cycle ergometry at 70-110% of critical power. The participants also completed a control condition in which no cycling was performed. Plasma lactate and ammonia were measured before and immediately after each strength test. Isokinetic, isometric and isotonic leg extension torques were not significantly different 8 or 32 h after endurance exercise compared with the control condition ( P > 0.05). A large (50.3%), but not statistically significant, increase in plasma ammonia was evident during the strength tests performed 8 h after endurance exercise, while a significant ( P ? 0.05) increase in ammonia was also seen 32 h after endurance exercise. No significant changes in plasma ammonia were evident in the control condition. Our results suggest that leg extension strength was not compromised by an earlier bout of endurance cycling. However, metabolic activity during the strength tests might have been altered by the preceding bout of endurance exercise.     

Changes in leg strength 8 and 32 h after endurance exercise

The aim of this study was to determine the effects of a single bout of endurance exercise on subsequent strength performance. Eight males with a long history of resistance training performed isokinetic, isometric and isotonic leg extension strength tests 8 and 32 h after 50 min of cycle ergometry at 70-110% of critical power. The participants also completed a control condition in which no cycling was performed. Plasma lactate and ammonia were measured before and immediately after each strength test. Isokinetic, isometric and isotonic leg extension torques were not significantly different 8 or 32 h after endurance exercise compared with the control condition (P > 0.05). A large (50.3%), but not statistically significant, increase in plasma ammonia was evident during the strength tests performed 8 h after endurance exercise, while a significant (P < 0.05) increase in ammonia was also seen 32 h after endurance exercise. No significant changes in plasma ammonia were evident in the control condition. Our results suggest that leg extension strength was not compromised by an earlier bout of endurance cycling. However, metabolic activity during the strength tests might have been altered by the preceding bout of endurance exercise.