Effects of Blood Flow Restricted Low-Intensity Concentric or Eccentric Training on Muscle Size and Strength

We investigated the acute and chronic effects of low-intensity concentric or eccentric resistance training with blood flow restriction (BFR) on muscle size and strength. Ten young men performed 30% of concentric one repetition maximal dumbbell curl exercise (four sets, total 75 reps) 3 days/week for 6 weeks. One arm was randomly chosen for concentric BFR (CON-BFR) exercise only and the other arm performed eccentric BFR (ECC-BFR) exercise only at the same exercise load. During the exercise session, iEMG for biceps brachii muscles increased progressively during CON-BFR, which was greater (p<0.05) than that of the ECC-BFR. Immediately after the exercise, muscle thickness (MTH) of the elbow flexors acutely increased (p<0.01) with both CON-BFR and ECC-BFR, but was greater with CON-BFR (11.7%) (p<0.01) than ECC-BFR (3.9%) at 10-cm above the elbow joint. Following 6-weeks of training, MRI-measured muscle cross-sectional area (CSA) at 10-cm position and mid-upper arm (12.0% and 10.6%, respectively) as well as muscle volume (12.5%) of the elbow flexors were increased (p<0.01) with CON-BFR. Increases in muscle CSA and volume were lower in ECC-BFR (5.1%, 0.8% and 2.9%, respectively) than in the CON-BFR and only muscle CSA at 10-cm position increased significantly (p<0.05) after the training. Maximal voluntary isometric strength of elbow flexors was increased (p<0.05) in CON-BFR (8.6%), but not in ECC (3.8%). These results suggest that CON-BFR training leads to pronounced acute changes in muscle size, an index of muscle cell swelling, the response to which may be an important factor for promoting muscle hypertrophy with BFR resistance training.     

Strength/power augmentation subsequent to short-term training abstinence

Strength augmentation has been demonstrated in resistance-trained men subsequent to 4 days of training abstinence. However, this phenomenon was exhibited in an unusual circumstance in which the exercise test (seated heel raise) primarily involved an isolated skeletal muscle (soleus) that is normally comprised almost exclusively of 1 fiber type. It is unclear if similar results would be found for aggregate muscle actions. Therefore, a comparable study was designed with this in mind. Subjects were apparently healthy, young, strength-trained men (n = 25). All performed various tests of bench press strength at the beginning of their last standardized dynamic constant external resistance (DCER) training session. Subjects were subsequently randomly assigned to 1 of 4 groups and repeated the identical tests at intervals of either 2, 3, 4, or 5 days with no intervening training. Strength tests consisted of 1 repetition maximum (1RM) concentric-only isokinetic bench presses performed at 1.49 and 0.37 m.s(-1) as well as a 1RM DCER bench press. Measures of peak force and power were obtained from the isokinetic tests and maximum load from the DCER test. Results were expressed in both absolute and relative (to body weight) terms. Subsequent to the 4 abstinence intervals, groups performed similarly (p > 0.05) for all dependent variables. Concurrently, however, a small effect size (ES) was found for the group having a 4-day respite for both absolute and relative expressions of peak force and power at the slowest isokinetic bench press velocity. A small ES was also identified for the group having 2 days of rest for relative peak force at the slowest isokinetic test velocity and for relative DCER strength. Therefore, modest and transient strength augmentation appears likely in aggregate muscle actions following 2-4 days of training abstinence in resistance-trained men, but only at relatively slow velocities.     

Musculoskeletal adaptations to 16 weeks of eccentric progressive resistance training in young women

We investigated the musculoskeletal adaptations and efficacy of a whole-body eccentric progressive resistance-training (PRT) protocol in young women. Subjects (n = 37; mean age, 24.3) were randomly assigned to one of 3 groups: high-intensity eccentric PRT (HRT), low-intensity eccentric PRT (LRT), or control. Subjects performed 3 sets of 6 repetitions at 125% intensity or 3 sets of 10 repetitions at 75% intensity in the HRT and LRT groups, respectively, 2 times per week for 16 weeks. Strength was determined by the concentric 1-repetition maximum (1RM) standard. Bone mass and body composition were measured by dual-energy x-ray absorptiometry (DXA). Blood and urine samples were obtained for deoxypyridinoline, osteocalcin, creatine kinase, and creatinine. Data were analyzed by repeated-measures analysis of variance with post hoc comparisons. Strength increased 20-40% in both training groups. Lean body mass increased in the LRT (0.7 +/- 0.6 kg) and HRT (0.9 +/- 0.9 kg) groups. Bone mineral content increased (0.855 +/- 0.958 g) in the LRT group only. Deoxypyridinoline decreased and osteocalcin increased in the HRT and LRT groups, respectively. These findings suggest that submaximal eccentric training is optimal for musculoskeletal adaptations and that the intensity of eccentric training influences the early patterns of bone adaptation.     

Role of concentric force in limiting improvement in muscular strength

We hypothesized that resistance training with combined eccentric and concentric actions, and concentric action only, should yield similar changes in muscular strength. Subjects in a free weight group trained three times a week for 12 wk with eccentric and concentric actions (FW, n = 16), a second group trained with concentric-only contractions using hydraulic resistance (HY; n = 12), and a control group did not train (n = 11). Training for FW and HY included five sets of supine bench press and upright squat at an intensity of 1-6 repetition maximum (RM) plus five supplementary exercises at 5-10 RM for a total of 20 sets per session for approximately 50 min. Testing at pre-, mid-, and posttraining included 1) 1 RM bench press and squat with and 2) without prestretch using free weights; 3)isokinetic peak force and power for bench press and squat at 5 degrees/s, and isotonic peak velocity and power for bench press with 20-kg load and squat with 70-kg load; 4) hydraulic peak bench press force and power, and peak knee extension torque and power at fast and slow speeds; and 5) surface anthropometry (fatfolds and girths to estimate upper arm and thigh volume and muscle area). Changes in overall fatness, muscularity, and muscle + bone cross-sectional area of the limbs did not differ between groups (P greater than 0.05). Improvements in free weight bench press and squat were similar (P greater than 0.05) in FW (approximately 24%) and HY (approximately 22%, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of eccentric strength testing on delayed-onset muscle pain

This investigation was designed to determine the effect of eccentric strength testing on delayed-onset muscle pain in 20 untrained university students. Initially, eccentric strength testing (5-repetition maximum [5RM]) was performed bilaterally. Next, 1 arm completed 3 sets of 10 eccentric repetitions to induce delayed-onset muscle pain. Then, in a subsequent session, whichever arm previously performed only the 5RM test completed the 5RM test a second time and the 3 sets of 10 eccentric repetitions. Statistical analyses supported significantly increased pain intensity and unpleasantness across 48 hours post-5RM test alone. However, pain intensity and unpleasantness after the eccentric training bouts were significantly lower in the arm that performed 2 5RM tests than the arm that performed only 1. Thus, the eccentric strength testing produced delayed-onset muscle pain and protected against future delayed-onset muscle pain. These effects should be considered when such testing is used in baseline strength assessments.     

Effects of low-load resistance training with vascular occlusion on the mechanical properties of muscle and tendon

The present study aimed to investigate the effects of low-load resistance training with vascular occlusion on the specific tension and tendon properties by comparing with those of high-load training. Nine participants completed 12 weeks (3 days/week) of a unilateral isotonic training program on knee extensors. One leg was trained using low load (20% of 1 RM) with vascular occlusion (LLO) and other leg using high load (80% of 1 RM) without vascular occlusion (HL). Before and after training, maximal isometric knee extension torque (MVC) and muscle volume were measured. Specific tension of vastus lateralis muscle (VL) was calculated from MVC, muscle volume, and muscle architecture measurements. Stiffness of tendon-aponeurosis complex in VL was measured using ultrasonography during isometric knee extension. Both protocols significantly increased MVC and muscle volume of quadriceps femoris muscle. Specific tension of VL increased significantly 5.5% for HL, but not for LLO. The LLO protocol did not alter the stiffness of tendon-aponeurosis complex in knee extensors, while the HL protocol increased it significantly. The present study demonstrated that the specific tension and tendon properties were found to remain following low-load resistance training with vascular occlusion, whereas they increased significantly after high-load training.     

Concentric and eccentric muscle strength before, during and after fatigue in 13 year-old boys

The purpose of this study was to investigate the force-producing characteristics of boys aged 13 years in relation to fatigue of elbow flexor muscles. Maximal voluntary force in elbow flexion was measured before and after a muscle endurance test (MET) by using an isokinetic dynamometer isometrically, concentrically and eccentrically at three velocities, i.e. 0.21, 0.52, and 1.05 rad · s^–1. The MET consisted of maximal concentric and eccentric muscle actions performed alternately at 0.52 rad · s^–1 for 50 consecutive trials. Muscle cross-sectional area (CSA) of elbow flexor muscles (biceps brachii and brachialis) was measured by a B-mode ultrasound apparatus. Although eccentric force showed significantly higher values than concentric force during MET, there was no significant difference in the rate of decline in force between the two actions. There was no significant difference in the rate of decline in force after MET for each velocity and muscle action. Isometric, concentric and eccentric force before MET was significantly related to muscle CSA whereas, after MET, concentric force significantly correlated with muscle CSA but there was no significant correlation between muscle CSA and isometric or eccentric force. From our study, it is therefore suggested that in development to maturity, isometric, concentric and eccentric force decrease at the same rate with advancing muscle fatigue; however, there might be differences among muscle actions in facors affecting force development.     

Microvascular architecture of the pampiniform plexus-testicular artery system in the rat: a scanning electron microscope study of corrosion casts

Because the architectural and biochemical properties of skeletal muscle dictate its force, velocity, and displacement properties, the major extensors (triceps brachii) and flexors (biceps brachii, brachialis, and brachioradialis) of the elbow in a primate (cynomolgus, monkey) were studied. Functional cross-sectional areas (CSA) were calculated from muscle mass, mean fiber length (normalized to a 2.20 microns sarcomere length), and angle of fiber pinnation measurements from each muscle. Fiber-type distributions were determined and used as a gross index of the biochemical capacities of the muscle. The extensor group had a shorter mean fiber length (31 vs. 47 mm), a larger CSA (13 vs. 8 cm2), and a higher overall percentage of slow-twitch fibers (47 vs. 26%). Consequently, the elbow extensors had a relatively greater potential for force production and force maintenance than the flexors. In contrast, the flexors were designed to optimize their length-velocity potentials; i.e., they had relatively long fibers and a higher fast-twitch fiber composition than the extensors. These morphologic differences between antagonistic muscle groups should be considered when evaluating the motor control mechanisms regulating reciprocal movements about the elbow.     

Effect of multiple-load training on the force-velocity relationship

The effect of training with a combination of different loads (multiple-load training) on the force-velocity and force-power relationships was examined with training programs that included maximal isometric contraction (Fmax) and concentric contraction of the elbow flexor muscles. Twenty-one male college students were placed into 3 equal training groups (G(30 + 60), G(30 + 100), and G(30 + 60 + 100)) and performed multiple-load training 3 days per week for 8 weeks. The training load was a set fraction of the maximal isometric strength (% Fmax). The G(30 + 60) group performed 6 repetitions of elbow flexion at 30 and 60% Fmax. The G(30 + 100) group performed 6 repetitions at 30% Fmax and six 5-second Fmax loads. The G(30 + 60 + 100) group performed 4 repetitions at 30 and 60% Fmax and four 5-second Fmax loads. After training, Fmax and maximal velocity significantly increased (p < 0.05) in all 3 training groups. The increases in maximal power were significantly (p < 0.05) different between the G(30 + 60 + 100) group (52.9%) and the G(30 + 100) group (24.2%). These results suggest that multiple-load training programs with 4-6 repetitions are effective for improving muscle power and velocity of the elbow flexors.     

Effects of two days of isokinetic training on strength and electromyographic amplitude in the agonist and antagonist muscles

The purpose of this study was to examine the effects of 2 days of isokinetic training of the forearm flexors and extensors on strength and electromyographic (EMG) amplitude for the agonist and antagonist muscles. Seventeen men (mean +/- SD age = 21.9 +/- 2.8 years) were randomly assigned to 1 of 2 groups: (a) a training group (TRN; n = 8), or (b) a control group (CTL; n = 9). The subjects in the TRN group were tested for maximal isometric and concentric isokinetic (randomly ordered velocities of 60, 180, and 300 degrees x s(-1)) torque of the dominant forearm flexors and extensors before (pretest) and after (posttest) 2 days of isokinetic strength training. Each training session involved 6 sets of 10 maximal concentric isokinetic muscle actions of the forearm flexors and extensors at a velocity of 180 degrees x s(-1). The subjects in the CTL group were also tested for strength but did not perform any training. Surface EMG signals were detected from the biceps brachii and triceps brachii muscles during the strength testing. The results indicated that there were no significant (p > 0.05) pre- to post-test changes in forearm flexion and extension torque or EMG amplitude for the agonist and antagonist muscles. Thus, unlike previous studies of the quadriceps femoris muscles, these findings for the forearm flexors and extensors suggested that 2 days of isokinetic training may not be sufficient to elicit significant increases in strength. These results may have implications for the number of visits that are required for rehabilitation after injury, surgery, or both.     

Power and work produced in different leg muscle groups when rising from a chair

The aim of this study was to determine the power output and work done by different muscle groups at the hip and knee joints during a rising movement, to be able to tell the degree of activation of the muscle groups and the relationship between concentric and eccentric work. Nine healthy male subjects rose from a chair with the seat at knee level. The moments of force about the hip and knee joints were calculated semidynamically. The power output (P) and work in the different muscle groups surrounding the joints was calculated as moment of force times joint angular velocity. Work was calculated as: work = f Pdt. The mean peak concentric power output was for the hip extensors 49.9 W, hip flexors 7.9 W and knee extensor 89.5 W. This power output corresponded to a net concentric work of 20.7 J, 1.0 J and 55.6 J, respectively. There was no concentric power output from the knee flexor muscles. Energy absorption through eccentric muscle action was produced by the hip extensors and hip flexors with a mean peak power output of 4.8 W and 7.4 W, respectively. It was concluded that during rising, the hip and knee muscles mainly worked concentrically and that the greatest power output and work were produced during concentric contraction of the knee and hip extensor muscles. There was however also a demand for eccentric work by the hip extensors as well as both concentric and eccentric work by the hip flexors. The knee flexor muscles were unloaded.     

Effects of whole-body low-intensity resistance training with slow movement and tonic force generation on muscular size and strength in young men

Our previous study showed that relatively low-intensity (approximately 50% one-repetition maximum [1RM]) resistance training (knee extension) with slow movement and tonic force generation (LST) caused as significant an increase in muscular size and strength as high-intensity (approximately 80% 1RM) resistance training with normal speed (HN). However, that study examined only local effects of one type of exercise (knee extension) on knee extensor muscles. The present study was performed to examine whether a whole-body LST resistance training regimen is as effective on muscular hypertrophy and strength gain as HN resistance training. Thirty-six healthy young men without experience of regular resistance training were assigned into three groups (each n = 12) and performed whole-body resistance training regimens comprising five types of exercise (vertical squat, chest press, latissimus dorsi pull-down, abdominal bend, and back extension: three sets each) with LST (approximately 55-60% 1RM, 3 seconds for eccentric and concentric actions, and no relaxing phase); HN (approximately 80-90% 1RM, 1 second for concentric and eccentric actions, 1 second for relaxing); and a sedentary control group (CON). The mean repetition maximum was eight-repetition maximum in LST and HN. The training session was performed twice a week for 13 weeks. The LST training caused significant (p < 0.05) increases in whole-body muscle thickness (6.8 +/- 3.4% in a sum of six sites) and 1RM strength (33.0 +/- 8.8% in a sum of five exercises) comparable with those induced by HN training (9.1 +/- 4.2%, 41.2 +/- 7.6% in each measurement item). There were no such changes in the CON group. The results suggest that a whole-body LST resistance training regimen is as effective for muscular hypertrophy and strength gain as HN resistance training.     

Strength conditioning in older men: skeletal muscle hypertrophy and improved function

The effects of strength conditioning on skeletal muscle function and mass were determined in older men. Twelve healthy untrained volunteers (age range 60-72 yr) participated in a 12-wk strength training program (8 repetitions/set; 3 sets/day; 3 days/wk) at 80% of the one repetition maximum (1 RM) for extensors and flexors of both knee joints. They were evaluated before the program and after 6 and 12 wk of training. Weekly measurements of 1 RM showed a progressive increase in strength in extensors and flexors. By 12 wk extensor and flexor strength had increased 107.4 (P less than 0.0001) and 226.7% (P less than 0.0001), respectively. Isokinetic peak torque of extensors and flexors measured on a Cybex II dynamometer increased 10.0 and 18.5% (P less than 0.05) at 60 degrees/s and 16.7 and 14.7% (P less than 0.05) at 240 degrees/s. The torque-velocity relationship showed an upward displacement of the curve at the end of training, mainly in the slow-velocity high-torque region. Midthigh composition from computerized tomographic scans showed an increase (P less than 0.01) in total thigh area (4.8%), total muscle area (11.4%), and quadriceps area (9.3%). Biopsies of the vastus lateralis muscle revealed similar increases (P less than 0.001) in type I fiber area (33.5%) and type II fiber area (27.6%). Daily excretion of urinary 3-methyl-L-histidine increased with training (P less than 0.05) by an average 40.8%. Strength gains in older men were associated with significant muscle hypertrophy and an increase in myofibrillar protein turnover.     

Effect of range of motion on muscle strength and thickness

The purpose of this investigation was to compare partial range-of-motion vs. full range-of-motion upper-body resistance training on strength and muscle thickness (MT) in young men. Volunteers were randomly assigned to 3 groups: (a) full range of motion (FULL; n = 15), (b) partial range of motion (PART; n = 15), or (c) control (CON; n = 10). The subjects trained 2 d · wk(-1) for 10 weeks in a periodized program. Primary outcome measures included elbow flexion maximal strength measured by 1 repetition maximum (1RM) and elbow flexors MT measured by ultrasound. The results indicated that elbow flexion 1RM significantly increased (p < 0.05) for the FULL (25.7 ± 9.6%) and PART groups (16.0 ± 6.7%) but not for the CON group (1.7 ± 5.5%). Also, FULL 1RM strength was significantly greater than the PART 1RM after the training period. Average elbow flexor MT significantly increased for both training groups (9.65 ± 4.4% for FULL and 7.83 ± 4.9 for PART). These data suggest that muscle strength and MT can be improved with both FULL and PART resistance training, but FULL may lead to greater strength gains.     

The utility of an empirically derived co-activation ratio for muscle force prediction through optimization

Biomechanical optimization models that apply efficiency-based objective functions often underestimate or negate antagonist co-activation. Co-activation assists movement control, joint stabilization and limb stiffness and should be carefully incorporated into models. The purposes of this study were to mathematically describe co-activation relationships between elbow flexors and extensors during isometric exertions at varying intensity levels and postures, and secondly, to apply these co-activation relationships as constraints in an optimization muscle force prediction model of the elbow and assess changes in predictions made while including these constraints. Sixteen individuals performed 72 isometric exertions while holding a load in their right hand. Surface EMG was recorded from elbow flexors and extensors. A co-activation index provided a relative measure of flexor contribution to total activation about the elbow. Parsimonious models of co-activation during flexion and extension exertions were developed and added as constraints to a muscle force prediction model to enforce co-activation. Three different PCSA data sets were used. Elbow co-activation was sensitive to changes in posture and load. During flexion exertions the elbow flexors were activated about 75% MVC (this amount varied according to elbow angle, shoulder flexion and abduction angles, and load). During extension exertions the elbow flexors were activated about 11% MVC (this amount varied according to elbow angle, shoulder flexion angle and load). The larger PCSA values appeared to be more representative of the subject pool. Inclusion of these co-activation constraints improved the model predictions, bringing them closer to the empirically measured activation levels.     

The influence of varying oxygen tensions in inspired gas on 133Xenon muscle clearance and fatigue levels during sustained and dynamic conctractions.

Isometric and isotonic endurance levels of both elbow flexors and knee extensors were tested during inspired gas mixtures of ca. 10%, 21% or 100% oxygen in nitrogen. The four work loads were set a 25, 50, 60 and 70% of maximal volitional isometric strength (IS). The isotonic exercise routine was carried out using weight lifting techniques of 20 repetitions per min from 75 degrees to 105 degrees of elbow flexion and knee extensions respectively. Prior to, during, and after the endurance experiments 133Xe clearance was monitored by light weight scintillation counters. A depot of 0.1 to 0.2 ml of isotonic saline containing 50 to 150 muCi of the isotope was used as an intramuscular tracer. The exercise clearance values varied inversely to the test load during isometric exercise. Isotonic exercise for both elbow flexors and knee extensors showed increasing clearance values up to 60% IS. Above this level a decrease in total clearance was recorded. Oxygen tension had no statistical effect on the clearance values. However, the relatively large scatter of the 133Xe clearance method, and an inhomogenous perfusion of skeletal muscle may have masked any anticipated effect of the various O2 tensions. Variations due to the raised intramuscular pressure appeared to be much more dominant than the hypothezised variation due to the 3 set oxygen tensions.     

Specificity of resistance training responses in neck muscle size and strength

This study examined hypertrophy after head extension resistance training to assess which muscles of the complicated cervical neuromuscular system were used in this activity. We also determined if conventional resistance exercises, which are likely to evoke isometric action of the neck, induce generalized hypertrophy of the cervical muscle. Twenty-two active college students were studied. [mean (SE) age, weight and height: 21 (1) years, 71 (4) kg and 173 (3) cm, respectively]. Subjects were assigned to one of three groups: RESX (head extension exercise and other resistance exercises), RES (resistance exercises without specific neck exercise), or CON (no training). Groups RESX (n = 8) and RES (n = 6) trained 3 days/week for 12 weeks with large-muscle mass exercises (squat, deadlift, push press, bent row and mid-thigh pull). Group RESX also performed three sets of ten repetitions of a head extension exercise 3 days/week with a load equal to the 3 × 10 repetition maximum (RM). Group CON (n = 8) was a control group. The cross-sectional area (CSA) of nine individual muscles or muscle groups was determined by magnetic resonance imaging (MRI) of the cervical region. The CSA data were averaged over four contiguous transaxial slices in which all muscles of interest were visible. The 3 × 10 RM for the head extension exercise increased for RESX after training [from 17.9 (1.0) to 23.9 (1.4) kg, P < 0.05] but not for RES [from 17.6 (1.4) to 17.7 (1.9)␣kg] or CON [from 10.1 (2.2) to 10.3 (2.1) kg]. RESX showed an increase in total neck muscle CSA after training [from 19.5 (3.0) to 22.0 (3.6) cm², P < 0.05], but RES and CON did not [from 19.6 (2.9) to 19.7 (2.9)␣cm² and 17.0 (2.5) to 17.0 (2.4) cm², respectively]. This hypertrophy for RESX was due mainly to increases in CSA of 23.9 (3.2), 24.0 (5.8), and 24.9 (5.3)% for the splenius capitis, and semispinalis capitis and cervicis muscles, respectively. The lack of generalized neck muscle hypertrophy in RES was not due to insufficient training. For example, the CSA of their quadriceps femoris muscle group, as assessed by MRI, increased by 7 (1)% after this short-term training (P < 0.05). The results suggest that: (1) the splenius capitis, and semispinalis capitis and cervicis muscles are mainly responsible for head extension; (2) short-term resistance training does not provide a sufficient stimulus to evoke neck muscle hypertrophy unless specific neck exercises are performed; and (3) the postural role of head extensors provides modest loading in bipeds. Accepted: 15 October 1996     

Early-phase strength gains during traditional resistance training compared with an upper-body air-resistance training device

The purpose of this study was to examine the early-phase adaptations of traditional dynamic constant external resistance (DCER) training vs. a portable upper-body training device (Fortex). The Fortex is a concentric training device based on air resistance. Contractions using this device are slow (1.5-3 s) and have a limited range of motion. The exercises potentially allow maximal muscle action during each contraction. Healthy, sedentary men (n = 30) were assigned to begin either 8 weeks of weight training (W, n = 12) or 8 weeks of Fortex training (F, n = 9), and were compared with a control group (C, n = 9). Exercises were chosen for the W group that would train similar muscle groups and contain a similar volume of repetitions as the F group. However, movement patterns and force curves were not identical. Increases in the upper-arm cross-sectional area were not detected in any of the groups. Both training groups showed strength gains in the various strength tests that were distinct from each other. Our results indicate that both Fortex and DCER training proved effective in eliciting strength gains in sedentary men over an 8-week training period. There are, however, limitations with the Fortex in terms of progression needs and training asymmetry that indicate it should be used as a complement to other training.     

Recovery Kinetics of Knee Flexor and Extensor Strength after a Football Match

We examined the temporal changes of isokinetic strength performance of knee flexor (KF) and extensor (KE) strength after a football match. Players were randomly assigned to a control (N = 14, participated only in measurements and practices) or an experimental group (N = 20, participated also in a football match). Participants trained daily during the two days after the match. Match and training overload was monitored with GPS devices. Venous blood was sampled and muscle damage was assessed pre-match, post-match and at 12h, 36h and 60h post-match. Isometric strength as well as eccentric and concentric peak torque of knee flexors and extensors in both limbs (dominant and non-dominant) were measured on an isokinetic dynamometer at baseline and at 12h, 36h and 60h after the match. Functional (KF_ecc/KE_con) and conventional (KF_con/KE_con) ratios were then calculated. Only eccentric peak torque of knee flexors declined at 60h after the match in the control group. In the experimental group: a) isometric strength of knee extensors and knee flexors declined (P<0.05) at 12h (both limbs) and 36h (dominant limb only), b) eccentric and concentric peak torque of knee extensors and flexors declined (P<0.05) in both limbs for 36h at 60°/s and for 60h at 180°/s with eccentric peak torque of knee flexors demonstrating a greater (P<0.05) reduction than concentric peak torque, c) strength deterioration was greater (P<0.05) at 180°/s and in dominant limb, d) the functional ratio was more sensitive to match-induced fatigue demonstrating a more prolonged decline. Discriminant and regression analysis revealed that strength deterioration and recovery may be related to the amount of eccentric actions performed during the match and athletes'' football-specific conditioning. Our data suggest that recovery kinetics of knee flexor and extensor strength after a football match demonstrate strength, limb and velocity specificity and may depend on match physical overload and players'' physical conditioning level.     

Difference in kinematics and kinetics between high- and low-velocity resistance loading equated by volume: implications for hypertrophy training

Although it is generally accepted that a high load is necessary for muscle hypertrophy, it is possible that a low load with a high velocity results in greater kinematics and kinetics than does a high load with a slow velocity. The purpose of this study was to determine if 2 training loads (35 and 70% 1 repetition maximum [1RM]) equated by volume, differed in terms of their session kinematic and kinetic characteristics. Twelve subjects were recruited in this acute randomized within-subject crossover design study. Two bouts of a half-squat exercise were performed 1 week apart, one with high load-low velocity (HLLV = 3 sets of 12 reps at 70% 1RM) and the other with low-load high-velocity (LLHV = 6 sets of 12 reps at 35% 1RM). Time under tension (TUT), average force, peak force (PF), average power (AP), peak power (PP), work (TW), and total impulse (TI) were calculated and compared between loads for the eccentric and concentric phases. For average eccentric and concentric single repetition values, significantly (p < 0.05) greater (～15-22%) PP outputs were associated with the LLHV loading, whereas significantly greater (～7-61%) values were associated with the HLLV condition for most other variables of interest. However, in terms of total session kinematics and kinetics, the LLHV protocol resulted in significantly greater (～16-61%) eccentric and concentric TUT, PF, AP, PP, and TW. The only variable that was significantly greater for the HLLV protocol than for the LLHV protocol was TI (～20-24%). From these results, it seems that the LLHV protocol may offer an equal if not better training stimulus for muscular adaptation than the HLLV protocol, because of the greater time under tension, power, force, and work output when the total volume of the exercise is equated.