Effect of PNF stretching training on the properties of human muscle and tendon structures

The purpose of this study was to investigate the influence of a 6‐week proprioceptive neuromuscular facilitation (PNF) stretching training program on the various parameters of the human gastrocnemius medialis muscle and the Achilles tendon. Therefore, 49 volunteers were randomly assigned into PNF stretching and control groups. Before and after the stretching intervention, we determined the maximum dorsiflexion range of motion (RoM) with the corresponding fascicle length and pennation angle. Passive resistive torque (PRT) and maximum voluntary contraction (MVC) of the musculo‐articular complex were measured with a dynamometer. Muscle‐tendon junction (MTJ) displacement allowed us to determine the length changes in tendon and muscle, and hence to calculate stiffness. Mean RoM increased from 31.1 ± 7.2° to 33.1 ± 7.2° (P = 0.02), stiffness of the tendon decreased significantly in both active (from 21.1 ± 8.0 to 18.1 ± 5.5 N/mm) and passive (from 12.1 ± 4.9 to 9.6 ± 3.2 N/mm) conditions, and the pennation angle increased from 18.5 ± 1.8° to 19.5 ± 2.1° (P = 0.01) at the neutral ankle position (90°), only in the intervention group, whereas MVC and PRT values remained unchanged. We conclude that a 6‐week PNF stretching training program increases RoM and decreases tendon stiffness, despite no change in PRT.     

Effect of proprioceptive neuromuscular facilitation stretching on the plantar flexor muscle-tendon tissue properties

Proprioceptive neuromuscular facilitation (PNF) stretching programs have been shown to be the most effective stretching technique to increase the range of motion (ROM). The objective of this study was to examine the mechanism of effect of PNF stretching on changes in the ROM. Sixty-two healthy subjects were randomized into two groups: a PNF stretching group and a control group. The PNF group performed a 6-week stretching program for the calf muscles. Before and after this period, all subjects were evaluated for dorsiflexion ROM, passive resistive torque (PRT) of the plantar flexors and stiffness of the Achilles tendon. The results of the study revealed that the dorsiflexion ROM was significantly increased in the PNF group (ΔROMext: 5.97±0.671°; ΔROMflex: 5.697±0.788°). The PRT of the plantar flexors and the stiffness of the Achilles tendon did not change significantly after 6 weeks of PNF stretching. These findings provide evidence that PNF stretching results in an increased ankle dorsiflexion. However, this increase in ROM could not be explained by a decrease of the PRT or by a change in stiffness of the Achilles tendon, and therefore can be explained by an increase in stretch tolerance.     

Minute oscillation stretching: A novel modality for reducing musculo‐tendinous stiffness and maintaining muscle strength

A novel stretching modality was developed to provide repetitive small length changes to the plantar flexors undergoing passive stretch defined as "minute oscillation stretching" (MOS). This study investigated the effects of MOS on neuromuscular activity during force production, the rate of torque development (RTD), and the elastic properties of the plantar flexors and Achilles tendon. Ten healthy males participated in this study. The neuromuscular activity of the triceps surae and tibialis anterior muscles during maximal voluntary plantar flexion torque [MVT], RTD of plantar flexion, Achilles tendon stiffness, and muscle stiffness were measured before and after two types of interventions for a total of 5 minutes: static stretching (SS) and MOS at 15 Hz and without intervention (control). Achilles tendon stiffness was calculated from the tendon elongation measuring by ultrasonography. Muscle stiffness was determined for the medial gastrocnemius [MG] using shear wave elastography. The MVT, mean electromyographic amplitudes [mEMG] of MG and lateral gastrocnemius [LG], and RTD were significantly decreased following SS (MVT: ?7.2 ± 7.9%; mEMG of MG: ?8.7 ± 10.2%; mEMG of LG: ?12.4 ± 10.5%; RTD: ?6.6 ± 6.8%), but not after MOS. Achilles tendon stiffness significantly decreased after SS (?13.4 ± 12.3%) and MOS (?9.7 ± 11.5%), with no significant differences between them. Muscle stiffness significantly decreased in SS and MOS, with relative changes being significantly greater for MOS (?7.9 ± 8.3%) than SS (?2.3 ± 2.9%) interventions. All variables remained unchanged in the controls. In conclusion, MOS changed muscle‐tendon compliance without loss of muscle function.     

Dynamic stretching is not detrimental to neuromechanical and sensorimotor performance of ankle plantarflexors

The acute effects of two dynamic stretching (DS) protocols on changes in the ankle range of motion (RoM), neuromechanical, and sensorimotor properties of the plantarflexor muscle group were examined. Eighteen participants received slow (SDS) or fast dynamic stretching (FDS) on two separate days. Outcome measures were assessed pre‐ and 2 minutes post‐interventions, and included maximum dorsiflexion angle, maximum isometric torque at neutral ankle position, maximum concentric and eccentric torques, force matching capacity, joint position sense and medial gastrocnemius muscle and tendon strain. Possibly and likely small increases in dorsiflexion RoM were observed after SDS (mean ± 90% confidence intervals; 1.8 ± 1.2°) and FDS (2.1 ± 1.2°), respectively. Very likely moderate decreases in muscle strain after SDS (?38.0 ± 20.6%) and possibly small decrease after FDS (?13.6 ± 21.2%) were observed. SDS resulted in a likely beneficial small increase in tendon strain (25.3 ± 29.7%) and a likely beneficial moderate increase after FDS (41.4 ± 44.9%). Effects on strength were inconsistent. Possibly small effect on positional error after SDS (?27.1 ± 37.5%), but no clear effect after FDS was observed. Both DS protocols increased RoM, and this was more due to an increase in tendon elongation rather than the muscle. However, SDS showed greater improvement than FDS in both neuromechanical and sensorimotor performance, and hence, SDS can be recommended as part of warm‐up in sporting contexts.     

Can chronic stretching change the muscle‐tendon mechanical properties? A review

It is recognized that stretching is an effective method to chronically increase the joint range of motion. However, the effects of stretching training on the muscle‐tendon structural properties remain unclear. This systematic review with meta‐analysis aimed to determine whether chronic stretching alter the muscle‐tendon structural properties. Published papers regarding longitudinal stretching (static, dynamic and/or PNF ) intervention (either randomized or not) in humans of any age and health status, with more than 2 weeks in duration and at least 2 sessions per week, were searched in PubMed, PED ro, ScienceDirect and ResearchGate databases. Structural or mechanical variables from joint (maximal tolerated passive torque or resistance to stretch) or muscle‐tendon unit (muscle architecture, stiffness, extensibility, shear modulus, volume, thickness, cross‐sectional area, and slack length) were extracted from those papers. A total of 26 studies were selected, with a duration ranging from 3 to 8 weeks, and an average total time under stretching of 1165 seconds per week. Small effects were seen for maximal tolerated passive torque, but trivial effects were seen for joint resistance to stretch, muscle architecture, muscle stiffness, and tendon stiffness. A large heterogeneity was seen for most of the variables. Stretching interventions with 3‐ to 8‐week duration do not seem to change either the muscle or the tendon properties, although it increases the extensibility and tolerance to a greater tensile force. Adaptations to chronic stretching protocols shorter than 8 weeks seem to mostly occur at a sensory level.     

Effects of plyometric training on passive stiffness of gastrocnemii and the musculo‐articular complex of the ankle joint

This study aimed to determine simultaneously the effects of plyometric training on the passive stiffness of the ankle joint musculo‐articular complex, the gastrocnemii muscle–tendon complex (MTC) and the Achilles tendon in order to assess possible local adaptations of elastic properties. Seventeen subjects were divided into a trained (TG) group and a control (CG) group. They were tested before and after 8 weeks of a plyometric training period. The ankle joint range of motion (RoM), the global musculo‐articular passive stiffness of the ankle joint, the maximal passive stiffness of gastrocnemii and the stiffness of the Achilles tendon during isometric plantar flexion were determined. A significant increase in the jump performances of TG relative to CG was found (squat jumps: +17.6%, P=0.008; reactive jumps: +19.8%, P=0.001). No significant effect of plyometric training was observed in the ankle joint RoM, musculo‐articular passive stiffness of the ankle joint or Achilles tendon stiffness (P>0.05). In contrast, the maximal passive stiffness of gastrocnemii of TG increased after plyometric training relative to CG (+33.3%, P=0.001). Thus, a specific adaptation of the gastrocnemii MTC occurred after plyometric training, without affecting the global passive musculo‐articular stiffness of the ankle joint.     

Effect of static and ballistic stretching on the muscle-tendon tissue properties

PURPOSE: Many studies have been undertaken to define the effects of static and ballistic stretching. However, most researchers have focused their attention on joint range-of-motion measures. The objective of the present study was to investigate whether static- and ballistic-stretching programs had different effects on passive resistive torque measured during isokinetic passive motion of the ankle joint and tendon stiffness measured by ultrasound imaging. METHODS: Eighty-one healthy subjects were randomized into three groups: a static-stretch group, a ballistic-stretch group, and a control group. Both stretching groups performed a 6-wk stretching program for the calf muscles. Before and after this period, all subjects were evaluated for ankle range of motion, passive resistive torque of the plantar flexors, and the stiffness of the Achilles tendon. RESULTS: The results of the study reveal that the dorsiflexion range of motion was increased significantly in all groups. Static stretching resulted in a significant decrease of the passive resistive torque, but there was no change in Achilles tendon stiffness. In contrast, ballistic stretching had no significant effect on the passive resistive torque of the plantar flexors. However, a significant decrease in stiffness of the Achilles tendon was observed in the ballistic-stretch group. CONCLUSION: These findings provide evidence that static and ballistic stretching have different effects on passive resistive torque and tendon stiffness, and both types of stretching should be considered for training and rehabilitation programs.     

Effects of tendon viscoelasticity in Achilles tendinosis on explosive performance and clinical severity in athletes

The aim was to compare viscoelastic properties of Achilles tendons between legs in elite athletes with unilateral tendinosis, and to investigate relationships between the properties and explosive performance and clinical severity. Seventeen male athletes (mean ± standard deviation age, 27.3 ± 2.0 years) who had unilateral, chronic middle‐portion tendinopathy of the Achilles tendon were assessed by the Victorian Institute of Sport Assessment questionnaire, measurements of tendon viscoelastic properties, voluntary electromechanical delay (EMD), normalized rate of force development (RFD), and one‐leg hopping distance. Compared with the non‐injured leg, the tendinopathic leg showed reduced tendon stiffness (?19.2%. P < 0.001), greater mechanical hysteresis (+21.2%, P = 0.004), lower elastic energy storage and release (?14.2%, P = 0.002 and ?19.1%, P < 0.001), lower normalized RFD at one‐fourth (?16.3%, P = 0.02), 2/4 (?17.3%, P = 0.006), and three‐fourths maximal voluntary contraction (?13.7%, P = 0.02), longer soleus and medial gastrocnemius voluntary EMD (+26.9%, P = 0.009 and +24.0%, P = 0.004), and shorter hopping distances (?34.1%, P < 0.001). Tendon stiffness was correlated with normalized RFD, voluntary EMD in the medial gastrocnemius, and hopping distances (r ranged from ?0.35 to 0.64, P < 0.05). Hysteresis was correlated to the soleus voluntary EMD and hopping distances (r = 0.42 and ?0.39, P < 0.05). We concluded that altered tendon viscoelastic properties in Achilles tendinosis affect explosive performance in athletes.     

Effects of warm‐up on hamstring muscles stiffness: Cycling vs foam rolling

This study investigated the effects of active and/or passive warm‐up tasks on the hamstring muscles stiffness through elastography and passive torque measurements. On separate occasions, fourteen males randomly completed four warm‐up protocols comprising Control, Cycling, Foam rolling, or Cycling plus Foam rolling (Mixed). The stiffness of the hamstring muscles was assessed through shear wave elastography, along with the passive torque‐angle relationship and maximal range of motion (ROM) before, 5, and 30 minutes after each experimental condition. At 5 minutes, Cycling and Mixed decreased shear modulus (?10.3% ± 5.9% and ?7.7% ± 8.4%, respectively; P≤.0003, effect size [ES]≥0.24) and passive torque (?7.17% ± 8.6% and ?6.2% ± 7.5%, respectively; P≤.051, ES≥0.28), and increased ROM (+2.9% ± 2.9% and +3.2% ± 3.5%, respectively; P≤.001, ES≥0.30); 30 minutes following Mixed, shear modulus (P=.001, ES=0.21) and passive torque (P≤.068, ES≥0.2) were still slightly decreased, while ROM increased (P=.046, ES=0.24). Foam rolling induced “small” immediate short‐term decreases in shear modulus (?5.4% ± 5.7% at 5 minutes; P=.05, ES=0.21), without meaningful changes in passive torque or ROM at any time point (P≥.12, ES≤0.23). These results suggest that the combined warm‐up elicited no acute superior effects on muscle stiffness compared with cycling, providing evidence for the key role of active warm‐up to reduce muscle stiffness. The time between warm‐up and competition should be considered when optimizing the effects on muscle stiffness.     

Central and peripheral fatigue in knee and elbow extensor muscles after a long‐distance cross‐country ski race

Although elbow extensors (EE) have a great role in cross‐country skiing (XC) propulsion, previous studies on neuromuscular fatigue in long‐distance XC have investigated only knee extensor (KE) muscles. In order to investigate the origin and effects of fatigue induced by long‐distance XC race, 16 well‐trained XC skiers were tested before and after a 56‐km classical technique race. Maximal voluntary isometric contraction (MVC) and rate of force development (RFD) were measured for both KE and EE. Furthermore, electrically evoked double twitch during MVC and at rest were measured. MVC decreased more in KE (?13%) than in EE (?6%, P = 0.016), whereas the peak RFD decreased only in EE (?26%, P = 0.02) but not in KE. The two muscles showed similar decrease in voluntary activation (KE ?5.0%, EE ?4.8%, P = 0.61) and of double twitch amplitude (KE ?5%, EE ?6%, P = 0.44). A long‐distance XC race differently affected the neuromuscular function of lower and upper limbs muscles. Specifically, although the strength loss was greater for lower limbs, the capacity to produce force in short time was more affected in the upper limbs. Nevertheless, both KE and EE showed central and peripheral fatigue, suggesting that the origins of the strength impairments were multifactorial for the two muscles.     

Effects of stretching on passive muscle tension and response to eccentric exercise

BACKGROUND: Stretching is used in an attempt to improve performance and reduce the risk of muscle injury, with little evidence to support its effectiveness. HYPOTHESIS: Four weeks of static or ballistic stretching can attenuate the increased soreness and decreased flexibility seen after eccentric exercise. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty-nine male subjects were randomly assigned to a static stretching, ballistic stretching, or control group. On each of 4 consecutive days, they completed 4 maximal range of motion stretches using a Cybex isokinetic dynamometer to passively stretch the hamstrings at 0.087 rad.s(-1) (5 deg.s(-1)). Stiffness from 0.87 to 1.48 rad (50 degrees -85 degrees ), peak range of motion, work absorption, peak resistive torque, and soreness were measured. Participants then completed 4 weeks of either static or ballistic stretching for a total stretching duration of 3600 seconds. After training, the 4 days of testing were repeated with an eccentric exercise task added after day 1. RESULTS: Stretching groups had an increase in range of motion and stretch tolerance after 4 weeks of stretching, with no change in muscle stiffness, work absorption, or delayed onset muscle soreness. After eccentric exercise, they also had greater range of motion and stretch tolerance than did controls. CONCLUSION: Both static stretching and ballistic stretching increase range of motion, most likely as a result of enhanced stretch tolerance rather than changes in muscle elasticity. Four weeks of stretching maintain range of motion and stretch tolerance in the days after eccentric exercise.     

Proprioceptive neuromuscular facilitation stretching : mechanisms and clinical implications

Proprioceptive neuromuscular facilitation (PNF) stretching techniques are commonly used in the athletic and clinical environments to enhance both active and passive range of motion (ROM) with a view to optimising motor performance and rehabilitation. PNF stretching is positioned in the literature as the most effective stretching technique when the aim is to increase ROM, particularly in respect to short-term changes in ROM. With due consideration of the heterogeneity across the applied PNF stretching research, a summary of the findings suggests that an 'active' PNF stretching technique achieves the greatest gains in ROM, e.g. utilising a shortening contraction of the opposing muscle to place the target muscle on stretch, followed by a static contraction of the target muscle. The inclusion of a shortening contraction of the opposing muscle appears to have the greatest impact on enhancing ROM. When including a static contraction of the target muscle, this needs to be held for approximately 3 seconds at no more than 20% of a maximum voluntary contraction. The greatest changes in ROM generally occur after the first repetition and in order to achieve more lasting changes in ROM, PNF stretching needs to be performed once or twice per week. The superior changes in ROM that PNF stretching often produces compared with other stretching techniques has traditionally been attributed to autogenic and/or reciprocal inhibition, although the literature does not support this hypothesis. Instead, and in the absence of a biomechanical explanation, the contemporary view proposes that PNF stretching influences the point at which stretch is perceived or tolerated. The mechanism(s) underpinning the change in stretch perception or tolerance are not known, although pain modulation has been suggested.     

Effect of acute static stretching on force, balance, reaction time, and movement time

PURPOSE: The purpose of the study was to investigate the effect of an acute bout of lower limb static stretching on balance, proprioception, reaction, and movement time. METHODS: Sixteen subjects were tested before and after both a static stretching of the quadriceps, hamstrings, and plantar flexors or a similar duration control condition. The stretching protocol involved a 5-min cycle warm-up followed by three stretches to the point of discomfort of 45 s each with 15-s rest periods for each muscle group. Measurements included maximal voluntary isometric contraction (MVC) force of the leg extensors, static balance using a computerized wobble board, reaction and movement time of the dominant lower limb, and the ability to match 30% and 50% MVC forces with and without visual feedback. RESULTS: There were no significant differences in the decrease in MVC between the stretch and control conditions or in the ability to match submaximal forces. However, there was a significant (P < 0.009) decrease in balance scores with the stretch (decreasing 9.2%) compared with the control (increasing 17.3%) condition. Similarly, decreases in reaction (5.8%) and movement (5.7%) time with the control condition differed significantly (P < 0.01) from the stretch-induced increases of 4.0% and 1.9%, respectively. CONCLUSION: In conclusion, it appears that an acute bout of stretching impaired the warm-up effect achieved under control conditions with balance and reaction/movement time.     

Time course of muscular, neural and tendinous adaptations to 23-day unilateral lower-limb suspension in young men

Muscles and tendons are highly adaptive to changes in chronic loading, though little is known about the adaptative time course. We tested the hypothesis that, in response to unilateral lower limb suspension (ULLS), the magnitude of tendon mechanical adaptations would match or exceed those of skeletal muscle. Seventeen men, (1.79±0.05 m, 76.6±10.3 kg, 22.3±3.8 years underwent ULLS for 23 days ( n =9) or acted as controls ( n =8). Knee extensors (KE) torque, voluntary activation (VA), cross-sectional area (CSA) (by magnetic resonance imaging), vastus lateralis fascicle length (Lf) and pennation angle (vartheta), patellar tendon stiffness and Young's modulus (by ultrasonography) were measured before, during and at the end of ULLS. After 14 and 23 days, (i) KE torque decreased by 14.8±5.5% and 21.0±7.1%, respectively ( P <0.001); (ii) VA did not change; (iii) KE CSA decreased by 5.2±0.7% ( P <0.001) and 10.0±2.0% ( P <0.001); Lf decreased by 5.9% (NS) and 7.7% ( P <0.05) and vartheta by 3.2% ( P <0.05) and, (iv) tendon stiffness and modulus decreased by 9.8±8.2% ( P <0.05) and 9.2±8.2% ( P <0.05) at 14 days, and by 29.3±11.5% ( P <0.005) and 30.1±11.9% ( P <0.01) at 23 days, with no changes in the controls. Hence, ULLS induces rapid losses of KE muscle size, architecture and function, but not in neural drive. Significant deterioration in tendon mechanical properties also occurs within 2 weeks, exacerbating in the third week of ULLS. Rehabilitation to limit muscle and tendon deterioration should probably start within 2 weeks of unloading.     

Effect of pelvic position and stretching method on hamstring muscle flexibility.

Hamstring muscle strain represents a significant injury to the athlete participating in sporting activities. Lack of hamstring flexibility has been correlated to hamstring muscle injury. There is, however, conflict concerning the most efficient hamstring stretching technique. The purpose of this study was to compare static stretch (SS) and proprioceptive neuromuscular facilitation (PNF) hamstring stretching techniques while maintaining the pelvis in two testing positions: anterior pelvic tilt (APT) or posterior pelvic tilt (PPT). Two groups of 10 subjects were randomly assigned to either an APT or PPT position. Each subject then performed eight sessions using PNF on one leg and SS on the other leg while maintaining the pelvis in the assigned position. Hamstring flexibility was assessed with the hip positioned at 90 degrees while actively extending the knee, i.e., active knee extension test (AKET). A two-way ANOVA comparing stretching technique and pelvic position revealed that the APT group significantly increased hamstring flexibility (P = 0.0375). There was not a significant difference between SS or PNF stretching technique in the APT position. There was not a significant increase in hamstring flexibility in the PPT group with either stretching technique (P > 0.05). The results suggest that APT position was more important than stretching method for increasing hamstring muscle flexibility.     

Effects of concurrent exercise training on muscle dysfunction and systemic oxidative stress in older people with COPD

Oxidative stress is associated with disease severity and limb muscle dysfunction in COPD. Our main goal was to assess the effects of exercise training on systemic oxidative stress and limb muscle dysfunction in older people with COPD. Twenty‐nine outpatients with COPD (66‐90 years) were randomly assigned to a 12‐week exercise training (ET; high‐intensity interval training (HIIT) plus power training) or a control (CT; usual care) group. We evaluated mid‐thigh muscle cross‐sectional area (CSA; computed tomography); vastus lateralis (VL) muscle thickness, pennation angle, and fascicle length (ultrasonography); peak VO₂ uptake (VO_2peak) and work rate (W_peak) (incremental cardiopulmonary exercise test); rate of force development (RFD); maximal muscle power (P_max; force‐velocity testing); systemic oxidative stress (plasma protein carbonylation); and physical performance and quality of life. ET subjects experienced changes in mid‐thigh muscle CSA (+4%), VL muscle thickness (+11%) and pennation angle (+19%), VO_2peak (+14%), W_peak (+37%), RFD (+32% to 65%), P_max (+38% to 51%), sit‐to‐stand time (?24%), and self‐reported health status (+20%) (all P < 0.05). No changes were noted in the CT group (P > 0.05). Protein carbonylation decreased among ET subjects (?27%; P < 0.05), but not in the CT group (P > 0.05). Changes in protein carbonylation were associated with changes in muscle size and pennation angle (r = ?0.44 to ?0.57), exercise capacity (r = ?0.46), muscle strength (r = ?0.45), and sit‐to‐stand performance (r = 0.60) (all P < 0.05). The combination of HIIT and power training improved systemic oxidative stress and limb muscle dysfunction in older people with COPD. Changes in oxidative stress were associated with exercise‐induced structural and functional adaptations.     

Non-uniform distribution of passive muscle stiffness within hamstring

Limited information is available on whether stiffness is different within and between the constituents of the hamstring, that is, the biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM). Therefore, understanding of hamstring injuries and stretching effect on hamstring stiffness is difficult. The present study primarily aimed to identify whether passive muscle stiffness differs between the BFlh, ST, and SM and between the proximal, middle, and distal sites within each muscle. Secondly, the effect of stretching exercise on the heterogeneity in passive muscle stiffness was examined. In the lengthened hamstring positions by extending the knee joint or flexing the hip joint, passive muscle shear modulus (a measure of stiffness) at the proximal, middle, and distal sites of the BFlh, ST, and SM was measured by using ultrasound shear wave elastography. Furthermore, before and after five repetitions of 90-seconds static stretching for the hamstring, passive muscle shear modulus at the proximal and distal sites of the SM was measured. The shear modulus was significantly higher in the SM than in the BFlh and ST and higher at the distal site than the proximal site in all muscles. After the stretching, the higher shear modulus at the distal site of the SM compared to the proximal site was still observed (pre-stretching: +80%, post-stretching: +81%). These findings indicate that passive muscle stiffness varies within the hamstring regardless of performing stretching exercise and that passive muscle stiffness is not highest at the proximal site of the SM where a stretching-type hamstring strain typically occurs.     

Postactivation potentiation can counteract declines in force and power that occur after stretching

Stretching can decrease a muscle's maximal force, whereas short but intense muscle contractions can increase it. We hypothesized that when combined, postactivation potentiation induced by reactive jumps would counteract stretch‐induced decrements in drop jump (DJ) performance. Moreover, we measured changes in muscle twitch forces and ankle joint stiffness (K_Ankle) to examine underlying mechanisms. Twenty subjects completed three DJs and 10 electrically evoked muscle twitches of the triceps surae subsequent to four different conditioning activities and control. The conditioning activities were 10 hops, 20s of static stretching of the triceps surae muscle, 20s of stretching followed by 10 hops, and vice versa. After 10 hops, twitch peak torque (TPT) was 20% and jump height 5% higher compared with control with no differences in K_Ankle. After stretching, TPT and jump height were both 9% and K_Ankle 6% lower. When hops and stretching were combined as conditioning activities, jump height was not different compared with control but significantly higher (11% and 8%) compared with stretching. TPTs were 16% higher compared with control when the hops were performed after stretching and 9% higher compared with the reverse order. K_Ankle was significantly lower when stretching was performed after the hops (6%) compared with control, but no significant difference was observed when hops were performed after stretching. These results demonstrate that conditioning hops can counteract stretch‐related declines in DJ performance. Furthermore, the differences in TPTs and K_Ankle between combined conditioning protocols indicate that the order of conditioning tasks might play an important role at the muscle–tendon level.     

Electromyostimulation training effects on neural drive and muscle architecture

PURPOSE: The purpose of the study was to investigate the effect of 4 and 8 wk of electromyostimulation (EMS) training on both muscular and neural adaptations of the knee extensor muscles. METHODS: Twenty males were divided into the electrostimulated group (EG, N = 12) and the control group (CG, N = 8). The training program consisted of 32 sessions of isometric EMS over an 8-wk period. All subjects were tested at baseline (B) and retested after 4 (WK4) and 8 (WK8) wk of EMS training. The EMG activity and muscle activation obtained under maximal voluntary contractions (MVC) was used to assess neural adaptations. Torque and EMG responses obtained under electrically evoked contractions, muscle anatomical cross-sectional area (ACSA), and vastus lateralis (VL) pennation angle, both measured by ultrasonography imaging, were examined to analyze muscular changes. RESULTS: At WK8, knee extensor MVC significantly increased by 27% (P < 0.001) and was accompanied by an increase in muscle activation (+6%, P < 0.01), quadriceps muscle ACSA (+6%, P < 0.001), and VL pennation angle (+14%, P < 0.001). A significant increase in normalized EMG activity of both VL and vastus medialis (VM) muscles (+69 and +39%, respectively, P < 0.001) but not of rectus femoris (RF) muscle was also found at WK8. The ACSA of the VL, VM, and vastus intermedius muscles significantly increased at WK8 (5-8%, P < 0.001) but not at WK4, whereas no changes occurred in the RF muscle. CONCLUSION: We concluded that the voluntary torque gains obtained after EMS training could be attributed to both muscular and neural adaptations. Both changes selectively involved the monoarticular vastii muscles.     

Massage induces an immediate,albeit short‐term,reduction in muscle stiffness

Using ultrasound shear wave elastography, the aims of this study were: (a) to evaluate the effect of massage on stiffness of the medial gastrocnemius (MG) muscle and (b) to determine whether this effect (if any) persists over a short period of rest. A 7‐min massage protocol was performed unilaterally on MG in 18 healthy volunteers. Measurements of muscle shear elastic modulus (stiffness) were performed bilaterally (control and massaged leg) in a moderately stretched position at three time points: before massage (baseline), directly after massage (follow‐up 1), and following 3 min of rest (follow‐up 2). Directly after massage, participants rated pain experienced during the massage. MG shear elastic modulus of the massaged leg decreased significantly at follow‐up 1 (?5.2 ± 8.8%, P = 0.019, d = ?0.66). There was no difference between follow‐up 2 and baseline for the massaged leg (P = 0.83) indicating that muscle stiffness returned to baseline values. Shear elastic modulus was not different between time points in the control leg. There was no association between perceived pain during the massage and stiffness reduction (r = 0.035; P = 0.89). This is the first study to provide evidence that massage reduces muscle stiffness. However, this effect is short lived and returns to baseline values quickly after cessation of the massage.