The effect of 5, 10, and 20 repetition maximums on the recovery of voluntary and evoked contractile properties

Maximal strength training has been reported to emphasize neural adaptations. The main objective of this study was to detect differences in muscle activation between 5, 10, and 20 repetition maximum (RM) sets. Fourteen subjects performed elbow flexion with 5, 10, and 20RM. Subjects were tested for maximum isometric force (maximal voluntary contraction [MVC]), twitch amplitude (peak twitch [Pt]), time to peak twitch (TPT), half relaxation time ((1/2) RT), electromyography (EMG), and muscle activation (interpolated twitch). Subjects were tested preexercise and 30 seconds, 1, 2, and 3 minutes postexercise. There were no significant differences in MVC, muscle activation, or antagonist/agonist EMG after 5, 10, or 20RM. However, greater RM did have a greater detrimental effect on twitch properties than fewer RM. Peak twitch was significantly (p = 0.004) less (32.08%) for the 20 than for the 5RM, whereas TPT shortened (p < 0.05) by 7.3 and 11.1% with 10 and 20RM vs. 5RM, respectively. Half relaxation time at 20RM was shortened (p < 0.05) by 20.6 and 25.4% compared with that at 5 and 10RM, respectively. MVC, muscle activation, and temporal twitch properties did not recover within 3 minutes of recovery. In conclusion, whereas 5RM did not produce greater muscle inactivation, twitch contractile properties were affected to a greater degree by a higher number of RM.     

Twitch potentiation after fatiguing exercise in man

Twitch potentiation was studied in the human triceps surae complex before and after intermittent maximal voluntary contractions or electrical stimulation at 20 Hz. Both forms of exercise were conducted with intact circulation for a maximum of 10 min or with circulatory occlusion until force output declined 50%. The relative potentiation was determined when a control twitch was compared to a twitch obtained after 5 s of maximal voluntary plantar flexion. The unpotentiated twitch torque (PT) and potentiated twitch torque (PT*) were reduced most severely after voluntary ischemic exercise (63.2% and 52.5% respectively, (P less than 0.001)). However, the relative potentiation (PT*/PT) immediately after voluntary ischemic exercise increased to 1.65 +/- 0.18 from 1.22 +/- 0.13 at rest. Both PT and PT* recovered quickly after exercise. At rest, twitch contraction time (CT) and one-half relaxation time (1/2 RT) in the unpotentiated twitch were longer than that of contraction (CT*) and one-half relaxation time (1/2 RT*) in the potentiated twitch. Following non-occluded exercise, CT, CT*, 1/2 RT and 1/2 RT* were shortened relative to rest. After ischemic exercise CT and CT* were shortened although 1/2 RT and 1/2 RT* increased relative to rest. Both CT* and 1/2 RT* quickly recovered to pre-exercise values by 5 min post-exercise. Ratios of potentiated/control twitch parameters were not altered after nonoccluded exercise, but were increased after ischemic exercise. These results suggest that the mechanisms of fatigue which depress voluntary torque and twitch and potentiated twitch torques, do not interfere with the extent of potentiation after fatiguing exercise.     

Elbow flexor evoked twitch contractile properties in untrained men and women and male bodybuilders

The influence of elbow joint angle on elbow flexor isometric evoked twitch contractile properties was assessed in 15 young women (F), 18 young men (M) and 11 male bodybuilders (BB). Measurements were made at elbow joint angles of 1.31, 1.57, 1.83, 2.09, 2.36, 2.62 and 2.88 rad (3.14 rad =180° =full extension). The largest peak twitch torque values [mean (SE) N · m] in F [3.77 (0.20)], M [10.38 (0.68)] and BB [11.38 (1.05)] occurred at 2.88 rad. Peak torque was progressively smaller at smaller joint angles, but the decline from 2.88 to 1.31 rad was greater in M (68%) and BB (76%) than F (59%). Thus, the magnitude of intergroup differences in peak twitch torque (PT) was joint angle dependent. Twitch time to peak torque (TPT) was influenced in a complex way by joint angle in the three groups; BB had the lowest values at small joint angles but the highest values at the largest angles. Half-relaxation time (HRT) generally increased from the smallest to largest joint angles in a pattern that did not differ significantly among the three groups. Maximum rates of twitch torque development and relaxation showed the same pattern of results as PT; indicating that these time-related measures were more sensitive to joint angle effects on PT than on TPT or HRT. The results of this study indicate that careful consideration should be given to the selection of joint angles in the measurement of evoked twitch contractile properties for the purpose of making group comparisons or investigating the effects of interventions such as training.     

Maintenance of myoglobin concentration in human skeletal muscle after heavy resistance training

The aim of this study was to determine the effects of 8 weeks of resistance training (RT) on the myoglobin concentration ([Mb]) in human skeletal muscle, and to compare the change in the [Mb] in two different RT protocols. The two types of protocol used were interval RT (IRT) of moderate to low intensity with a high number of repetitions and a short recovery time, and repetition RT (RRT) of high intensity with a low number of repetitions and a long recovery time. A group of 11 healthy male adults voluntarily participated in this study and were divided into IRT (n = 6) and RRT (n = 5) groups. Both training protocols were carried out twice a week for 8 weeks. At the completion of the training period, the one-repetition maximal force values and isometric force were increased significantly in all the subjects, by about 38.8% and 26.0%, respectively (P < 0.01). The muscle fibre composition was unchanged by the 8 weeks of training. The muscle fibre cross-sectional areas were increased significantly by both types of training in all fibre types (I, IIa and IIb, mean + 16.1 %, P < 0.05). The [Mb] showed no significant changes at the completion of the training [IRT from 4.63 (SD 0.63) to 4.48 (SD 0.72), RRT from 4.47 (SD 0.75) to 4.24 (SD 0.80) mg x g(-1) wet tissue] despite a significant decrease in citrate synthase activity [IRT from 5.27 (SD 1.45) to 4.49 (SD 1.48), RRT from 5.33 (SD 2.09) to 4.85 (SD 1.87) micromol x min(-1) x g(-1) wet tissue; P < 0.05] observed after both protocols. These results suggested that myoglobin and mitochondria enzymes were regulated by different mechanisms in response to either type of RT. Moreover, the maintained [Mb] in hypertrophied muscle should preserve oxygen transport from capillaries to mitochondria even when diffusion distance is increased.     

Occurrence of fatigue during sets of static squat jumps performed at a variety of loads

Research has identified that the optimal power load for static squat jumps (with no countermovement) is lower than the loads usually recommended for power training. Lower loads may permit the performance of additional repetitions before the onset of fatigue compared with heavier loads; therefore, the aim of this study was to determine the point of fatigue during squat jumps at various loads (0, 20, 40, 60% 1-repetition maximum [1RM]). Seventeen professional rugby league players performed sets of 6 squat jumps (with no countermovement), using 4 loading conditions (0, 20, 40, and 60% of 1RM back squat). Repeated measures analysis of variance revealed no significant differences (p > 0.05) in force, velocity, power, and displacement between repetitions, for the 0, 20, and 40% loading conditions. The 60% condition showed no significant difference (p > 0.05) in peak force between repetitions; however, velocity (1.12 + 0.10 and 1.18 + 0.11 m·s(-1)), power (3,385 + 343 and 3,617 + 396 W) and displacement (11.13 + 2.31 and 11.85 + 2.16 cm) were significantly (p < 0.02) lower during repetition 6 compared with repetition 2. These findings indicate that when performing squat jumps (with no countermovement) with a load <40% 1RM back squat, up to >6 repetitions can be completed without inducing fatigue and a minimum of 4-6 repetitions should be performed to achieve peak power output. When performing squat jumps (with no countermovement) with a load equal to the 60% 1RM only, 5 repetitions should be performed to minimize fatigue and ensure maintenance of velocity and power.     

The effects of different speed training protocols on sprint acceleration kinematics and muscle strength and power in field sport athletes

A variety of resistance training interventions are used to improve field sport acceleration (e.g., free sprinting, weights, plyometrics, resisted sprinting). The effects these protocols have on acceleration performance and components of sprint technique have not been clearly defined in the literature. This study assessed 4 common protocols (free sprint training [FST], weight training [WT], plyometric training [PT], and resisted sprint training [RST]) for changes in acceleration kinematics, power, and strength in field sport athletes. Thirty-five men were divided into 4 groups (FST: n = 9; WT: n = 8; PT: n = 9; RST: n = 9) matched for 10-m velocity. Training involved two 60-minute sessions per week for 6 weeks. After the interventions, paired-sample t-tests identified significant (p ≤ 0.05) within-group changes. All the groups increased the 0- to 5-m and 0- to 10-m velocity by 9-10%. The WT and PT groups increased the 5- to 10-m velocity by approximately 10%. All the groups increased step length for all distance intervals. The FST group decreased 0- to 5-m flight time and step frequency in all intervals and increased 0- to 5-m and 0- to 10-m contact time. Power and strength adaptations were protocol specific. The FST group improved horizontal power as measured by a 5-bound test. The FST, PT, and RST groups all improved reactive strength index derived from a 40-cm drop jump, indicating enhanced muscle stretch-shortening capacity during rebound from impacts. The WT group increased absolute and relative strength measured by a 3-repetition maximum squat by approximately 15%. Step length was the major limiting sprint performance factor for the athletes in this study. Correctly administered, each training protocol can be effective in improving acceleration. To increase step length and improve acceleration, field sport athletes should develop specific horizontal and reactive power.     

Effects of resistance training intensity on sleep quality and strength recovery in trained men: a randomized cross-over study

Resistance training (RT) variables can affect sleep quality, strength recovery and performance. The aim of this study was to examine the acute effect of RT leading to failure vs. non-failure on sleep quality (SQ), heart rate variability (HRV) overnight and one-repetition maximum (1-RM) performance 24 hours after training. Fifteen resistance-trained male athletes (age: 23.4 ± 2.4 years; height 178.0 ± 7.6 cm; weight: 78.2 ± 10.6 kg) performed two training sessions in a randomized order, leading to failure (4x10) or non-failure (5x8(10) repetitions), with 90 seconds for resting between sets at 75% 1-RM in bench press (BP) and half squat (HS). The day after, the participants completed the predicted 1-RM test for both exercises. In addition, the subjective and actigraphic SQ and HRV during sleep were measured after each training session. The day after the training protocol leading to failure, the 1-RM of BP (MD = 7.24 kg; -7.2%; p < 0.001) and HS (MD = 20.20 kg; -11.1%; p < 0.001) decreased. However, this parameter did not decrease after a non-failure RT session. No differences were observed between failure and non-failure training sessions on SQ and HRV; therefore, both types of training sessions similarly affected the SQ and the autonomic modulation during the night after the training session. This study provides an insight into the influence of different training strategies on SQ, strength performance and recovery after moderate- to high-demand training. This information could be useful especially for professional coaches, weightlifters and bodybuilders, due to the potential influence on the programming processes.     

Neuromuscular responses to different resistance loading protocols using pneumatic and weight stack devices

The purpose of this study was to examine single repetition characteristics and acute neuromuscular responses to typical hypertrophic (HL), maximal strength (MSL), and power (PL) loadings performed with two of the most common resistance modes; pneumatic and weight stack. Acute responses were assessed by measuring maximal voluntary contraction (MVC), corresponding quadriceps-EMG and resting and superimposed twitch torques. Activation level was calculated from the twitch torques.Decreases in MVC were greater during HL and MSL than during PL. During HL, resting twitch force decreased 8% (P < 0.05) more on the weight stack than on the pneumatic device. Furthermore, loading using the weight stack caused reduced resting twitch force, activation level, and EMG-amplitude after MSL and PL (P < 0.05–0.01).PL on the pneumatic device decreased MVC and rapid force production, while the respective PL on the weight stack device was specific to decreased rapid force production only. However, mean angular velocities and power of the repetitions were higher on the pneumatic device when using light loads.The present study showed that, at least in untrained subjects, the weight stack device induced greater levels of peripheral fatigue during HL. It also led to large central fatigue during MSL and PL. On the other hand, on the pneumatic device contraction velocity with low loads was higher compared to the weight stack device.Therefore, it is recommended that the resistance mode should be chosen according to the specific training goal.     

兔膈肌力学模式对慢性电刺激的适应性改变和细胞外Ca …

目的：研究兔膈肌肌条力学对不同频率慢性电刺激（ＣＥＳ）的适应性变化特征和细胞外Ｃａ＾２＋变化夺其力学特征的影响。方法：测定正常对照组和ＣＥＳ组的颤搐收缩张力（Ｐｔ）、峰值张力时间（ＴＰＴ）、１／２松弛时间（１／２ＲＴ）、强直颤搐收缩张力（Ｐｏ）、疲劳指数（ＦＩ）和疲劳恢复指数（ＦＲＩ）;观察在无Ｃａ＾２＋Ｈａｎｋ’ｓ液和标准Ｈａｎｋ’ｓ液时肌条收缩张力消失和恢复的时间差异。结果：①同对照组作比较,     

Early neural responses to strength training

The neural adaptations that accompany strength training have yet to be fully determined. Here we sought to address this topic by testing the idea that strength training might share similar mechanisms with some forms of motor learning. Since ballistic motor learning is accompanied by a shift in muscle twitches induced by transcranial magnetic stimulation (TMS) toward the training direction, we sought to investigate if these changes also occur after single isometric strength training sessions with various contraction duration and rate of force development characteristics (i.e., brief or sustained ballistic contractions or slow, sustained contractions). Twitch force resultant vectors and motor-evoked potentials (MEPs) induced by TMS were measured before and after single sessions of strength training involving the forearm muscles. Participants (n = 12) each performed three training protocols (each consisting of 4 sets of 10 repetitions) and served as their own control in a counterbalanced order. All three training protocols caused a significant (P < 0.05) shift in TMS-induced twitch force resultant vectors toward the training direction, followed by a gradual shift back toward the pretraining direction. The strongest effect was found when training involved both ballistic and sustained force components. There were no large or consistent changes in the direction of twitches evoked by motor nerve stimulation for any of the three training protocols. We suggest that these early neural responses to strength training, which share similar corticospinal changes to motor learning, might reflect an important process that precedes more long-term neural adaptation that ultimately enhance strength.     

Muscle activation strategies during strength training with heavy loading vs. repetitions to failure

Going to failure, or not, has probably been one of the most debated issues during the history of strength training. However, few studies have directly compared the physiological effect of failure vs. nonfailure strength training. The purpose of this study was to evaluate muscle activation strategies with electromyography (EMG) during heavy repetitions vs. repetitions to failure with lighter resistance. Fifteen healthy untrained women performed a set with heavy loading (3 repetition maximum [RM]) and a set of repetitions to failure with lower resistance (～15 RM) during lateral raise with elastic tubing. Electromyographic amplitude and median power frequency of specific shoulder and neck muscles were analyzed, and the BORG CR10 scale was used to rate perceived loading immediately after each set of exercise. During the failure set, normalized EMG was significantly lower during the first repetition and significantly higher during the latter repetitions compared with the heavy 3-RM set (p < 0.05). Normalized EMG for the examined muscles increased throughout the set to failure in a curvilinear fashion--e.g., for the trapezius from 86 to 124% maximal voluntary contraction (p < 0.001)--and reached a plateau during the final 3-5 repetitions before failure. Median power frequency for all examined muscles decreased throughout the set to failure in a linear fashion, indicating progressively increasing fatigue. In conclusion, going to complete failure during lateral raise is not necessary to recruit the entire motor unit pool in untrained women--i.e., muscle activity reached a plateau 3-5 repetitions from failure with an elastic resistance of approximately 15 RM. Furthermore, strengthening exercises performed with elastic tubing seem to be an efficient resistance exercise and a feasible and practical alternative to traditional resistance equipment.     

A comparison of adductor pollicis fatigue in older men and women

Sex differences in fatigue resistance of the adductor pollicis (AP) muscle were studied in 24 older adults who were divided into three groups: 12 older men (69.8 +/- 4.60 years), 6 older women not on hormone replacement therapy (HRT) (70.2 +/- 4.02 years), and 6 older women on HRT (68.7 +/- 6.47 years). Fatigue in the AP muscle was induced using an intermittent (5 s contraction, 5 s rest) submaximal voluntary contraction (50% of maximal voluntary contraction (MVC)) protocol, which was continued until exhaustion (i.e., when subjects could either no longer maintain a 5-s contraction at 50% MVC or when the MVC was deemed to be lower than the target force). There was no effect of HRT on MVC or time to fatigue (TTF); therefore, the older women were pooled as one subject group. At baseline, men were stronger than women for MVC (75.9 +/- 18.8 N in men vs. 56.8 +/- 10.0 N in women; P < 0.05) and evoked twitch force (7.3 +/- 1.7 N in men vs. 5.2 +/- 0.8 N in women; P < 0.05). There was no difference in TTF between men and women (14.77 +/- 7.06 min in men vs. 11.53 +/- 4.91 min in women; P > 0.20), nor was there a significant relationship between baseline muscle force and TTF (r = 0.14). There was also no difference in the pattern of fatigue and recovery between the men and women. These results suggest that there is no difference in endurance or fatigue characteristics of the AP muscle in men and women over the age of 65 years, and that baseline muscle force does not predict fatigue resistance in this muscle.     

Effect of resistive knee extension training on postural control measures in middle aged and elderly persons

The purpose of the present study was to determine whether knee extension strength gain in middle-aged and elderly persons is associated with improvement in the limits of stability when leaning his/her body in various directions. The resistance training group (EXT; 4 males, 17 females) completed two bilateral knee extension training sessions, consisting of one set of exercises, per week for 10 weeks. The non-training control group (CONT; 4 males, 3 females) were instructed not to train their legs during the 10-week control period. One set of exercises consisted of 8-12 repetitions of a dynamic resistance exercise until volitional fatigue for knee extension. The initial load for training was set at 70% of the one-repetition maximum (1-RM). The thickness of the rectus femoris (RF) and vastus lateralis (VL) muscles were measured using a B-mode ultrasound apparatus. The postural control measures, obtained using the Balance Master system, included the percentage limits-of-stability (%LOS) and path length (%Path). The 1-RM in EXT was increased significantly by resistance training (p < 0.001). In addition, significant differences were observed between the percentage increase of 1-RM in EXT and those in CONT at wk 5 and at wk 10 of resistance training (p < 0.001). However, no significant increase in muscle thickness of RF or VL was found in EXT. The %LOS to the rear target in EXT was increased significantly by resistance training (p < 0.05-0.01). In addition, the percentage change in %Path was decreased significantly by resistance training (p < 0.001). Therefore, strength gain in quadriceps femoris appears to be associated with improvement in the %LOS and %Path for the rear. In conclusion, strength gain in quadriceps femoris is thought to possibly enable accurate movement of the COG farther from the center target towards the rear, suggesting that strength gain has a positive influence on a person's perception of their ability to avoid falls.     

去负荷小鼠比目鱼肌收缩特性和纤维类型转化

目的:探讨去负荷后小鼠比目鱼肌的收缩特性与骨骼肌纤维类型转化之间的关系。方法:采用离体肌肉灌流技术和电刺激方法,在小鼠后肢去负荷28 d引起骨骼肌萎缩后,观察比目鱼肌单收缩、强直收缩能力和肌疲劳指标等收缩特性的改变,同时利用组织免疫荧光染色和实时定量聚合酶链式反应(real-time PCR)等技术检测去负荷后比目鱼肌快慢肌纤维组成和纤维类型转化的变化。结果:去负荷28 d后,小鼠比目鱼肌单收缩力、强直收缩能力和疲劳指数(fatigue index)均有显著性下降,同时伴有快肌纤维亚型的增加和慢肌纤维亚型的减少。结论:去负荷28 d后小鼠比目鱼肌收缩特性的改变和快慢肌纤维类型的转化有关。     

Effect of acute hypercapnia on limb muscle contractility in humans

The effect of acute hypercapnia on skeletal muscle contractility and relaxation rate was investigated. The contractile force of fresh and fatigued quadriceps femoris (QF) and adductor pollicis (AP) was studied in normal humans by use of electrical stimulation. Maximum relaxation rate from stimulated contractions was measured for both muscles. Acute hypercapnia led to a rapid substantial reduction of contraction force. The respiratory acidosis after 9% CO2 was breathed for 20 min [mean venous blood pH 7.26 and end-tidal PCO2 (PETCO2) 65.1 Torr] reduced 20- and 100-Hz stimulated contractions of QF to 72.8 +/- 4.4 and 80.0 +/- 5.1% of control values, respectively. After 8 and 9% CO2 were breathed for 12 min, AP forces at 20- and 50-Hz stimulation were also reduced. Twitch tension of AP was reduced by a mean of 25.5% when subjects breathed 9% CO2 for 12 min [mean arterialized venous blood pH (pHav) 7.25 and PETCO2 66 Torr]. Over the range of 5% (pHav 7.38 and PETCO2 47 Torr) to 9% CO2, there was a linear relationship between twitch tension loss and pHav, arterialized venous blood PCO2, and PETCO2. Acute respiratory acidosis (mean PETCO2 61 Torr) increased the severity of low-frequency fatigue after intermittent voluntary contractions of AP. At 20 min of recovery, twitch tension was 63.2 +/- 13.4 and 46.8 +/- 16.4% of control value after exercise breathing air and 8% CO2, respectively. Acute hypercapnia (mean PETCO2 65.1 and 60.5 Torr) did not alter the maximum relaxation rate from tetanic contractions of fresh QF and from twitch tensions of AP.     

Effects of halothane on mechanical response of skeletal muscle from malignant hyperthermia susceptible patients.

The purpose of this investigation was to compare the effects of halothane on malignant hyperthermia (MH) and normal isolated muscle bundle performance during isometric contraction and relaxation phases. Mechanical parameters were measured: peak tension (PT), time to peak tension (TPT) and positive peak of isometric tension derivative (+dP/dtmax) characterized the contraction phase. Half-relaxation time (RT1/2) and negative peak of isometric tension derivative (-dP/dtmax) characterized the relaxation phase. The ratio R = (+dP/dtmax)/(-dP/dtmax) was used to study the coupling between contraction and relaxation under isometric condition. In normal muscle, halothane increased PT by nearly 40% without altering TPT. The +dP/dtmax value increased concomitantly with the -dP/dtmax values, thus no changes in R was observed. In MH muscle, PT was first potentiated (0.5-1.0 vol% halothane) and then depressed (2.0-3.0 vol% halothane). TPT and +dP/dtmax were not altered whereas RT1/2 increased progressively with concomitant decrease in -dP/dtmax, thus R increased by nearly 40%. The amplitude of MH muscle contracture with stepwise concentrations of halothane was correlated with the increase of RT1/2 and R, and the decrease of -dP/dtmax. These results suggest that halothane alters the relaxation phase more than the contraction phase in MH human skeletal muscle compared to normal muscle.     

Reversal of muscle fatigue during 16 h of heavy intermittent cycle exercise.

This study examined the effects of extended sessions of heavy intermittent exercise on quadriceps muscle fatigue and weakness. Twelve untrained volunteers (10 men and 2 women), with a peak oxygen consumption of 44.3 +/- 2.3 ml.kg(-1).min(-1), exercised at approximately 91% peak oxygen consumption for 6 min once per hour for 16 h. Muscle isometric properties assessed before and after selected repetitions (R1, R2, R4, R7, R12, and R15) were used to quantitate fatigue (before vs. after repetitions) and weakness (before vs. before repetitions). Muscle fatigue at R1 was indicated by reductions (P < 0.05) in peak twitch force (135 +/- 13 vs. 106 +/- 11 N) and by a reduction (P < 0.05) in the force-frequency response, which ranged between approximately 53% at 10 Hz (113 +/- 12 vs. 52.6 +/- 7.4 N) and approximately 17% at 50 Hz (324 +/- 27 vs. 270 +/- 30 N). No recovery of force, regardless of stimulation frequency, was observed during the 54 min between R1 and R2. At R2 and for all subsequent repetitions, no reduction in force, regardless of stimulation frequency, was generally found after the exercise. The only exception was for R2, where, at 20 Hz, force was reduced (P < 0.05) by 18%. At R15, force before repetitions for high frequencies (i.e., 100 Hz) returned to R1 (333 +/- 29 vs. 324 +/- 27 N), whereas force at low frequency (i.e., 10 Hz) was only partially (P < 0.05) recovered (113 +/- 12 vs. 70 +/- 6.6 N). It is concluded that multiple sessions of heavy exercise can reverse the fatigue noted early and reduce or eliminate weakness depending on the frequency of stimulation.     

Physiological responses using 2 high-speed resistance training protocols

This study compared physiological responses to 2 high-speed resistance training (RT) protocols in untrained adults. Both RT protocols included 12 repetitions for the same 6 exercises, only differing in continuous (1 x 12) or discontinuous (2 x 6) mode. For discontinuous mode, there was a 15-second rest interval between sets. We hypothesized that the 2 x 6 protocol was less physiologically demanding than the 1 x 12 protocol. Fifteen untrained adults randomly performed the protocols on 2 different days while heart rate (HR), blood lactate (BL), rate of perceived exertion (RPE), and concentric phase mean power (CPMP) were measured. Significantly lower values (mean +/- SE) were seen with the discontinuous protocol for exercise HR (119 +/- 5 vs. 124 +/- 5 b x min(-1)), BL (5.7 +/- 0.5 vs. 6.7 +/- 0.3 mMol/L), and RPE (5.4 +/- 0.3 vs. 5.8 +/- 0.4) (p < 0.05). CPMP tended to be higher in the discontinuous protocol, especially for the 2 last repetitions. The discontinuous protocol was significantly less physiologically demanding, although similar or higher CPMP values were obtained. These findings may help foster long-term adherence to RT in untrained individuals. However, future studies are needed to compare physiological adaptations induced by these 2 RT protocols.     

Muscle function in children

Electrically evoked mechanical and contractile properties of the triceps surae have been measured in 52 children aged 11 and 14 years, and results compared with previously reported data for adults (Davies and White 1982). The results show that the time to peak tension (TPT), half relaxation time (1/2RT) and supramaximal tension (Pt) of the twitch were not significantly (P greater than 0.1) different in girls and boys and independent of age. The 14-year-old girls and boys were stronger in terms of their supramaximal 10, 20, and 50 Hz tetanic tensions and maximal voluntary contraction (MVC) than their younger counterparts, and both groups of children were significantly (P less than 0.001) weaker than the young adults. However, if standardisation was made for an anthropometric estimate of calf muscle (plus bone) cross-sectional area (CSA), the differences in strength disappeared. Electrically stimulated and voluntary maximal force per unit CSA measured at the knee were 17.1 and 20.5 N X cm2 respectively and independent of sex and age. The loss of force during a 2-min stimulated fatigue test was the same in the children as the adults. The average fatigue indices ranged from 0.52 to 0.72 in the children, compared with 0.68 in the adults. It is concluded that absolute differences in muscle strength in children are a function of muscle mass. The force generating capacity expressed in N X cm2, fatiguability, contraction and relaxation times of the triceps surae would appear to remain unchanged through adolescence and early adulthood.