Stretching of voluntarily-activated muscles evokes greater acute and chronic adaptive changes than (traditional) static stretching

Purpose: To determine whether acute (single session) and chronic (prolonged training) increases in joint range of motion(ROM) are greater if muscles are voluntarily activated before being stretched (i.e. active muscle stretching) when compared to traditional, static stretching. Methods: In experiment 1, 18 physically-active subjects completed two static (SS1, SS2) and active (AMS1, AMS2) calf muscle stretch sessions, with each session separated by 48–72h. SS sessions comprised 5 sets of 30-s static stretches, whilst AMS comprised 5 sets of 10 repetitions of 3-s stretches imposed on maximally contracted muscle (both interventions=150s). In experiment 2, 13 subjects performed twice-weekly AMS for 6 weeks (5×12 repetitions, 3-s maximally-active muscle stretches 10◦/s, 20◦ plantarflexion to 10◦ dorsiflexion) on an isokinetic dynamometer. Maximal isometric plantarflexor strength, dorsiflexion ROM, peak passive tension, and muscle, tendon and muscle-tendon unit (MTU) stiffness were measured using isokinetic dynamometry, real-time ultrasound and 3D motion analyses before and after both the acute (experiment 1) and chronic (experiment 2) interventions. Results: In experiment 1, a significantly greater increase in ROM was observed in AMS (5.9–7.7◦) than SS (2.2–3.0◦), with ROM significantly greater after AMS2 than all other trials (+3.3–5.8◦). A significant ROM increase was already detected after the first set in AMS trials (2.2–3.1◦), and this was similar to the magnitude of change after 5 sets of SS. Similar decreases in the passive moment slope occurred after SS (7.3–11.7%) and AMS (10.1–15.3%), how-ever significant increases in peak passive moment (30.7–34.7%) and elastic energy storage (54.3–68.2%) occurred only after AMS. A significant reduction in maximal isometric strength occurred only after SS1 (6.5%). In experiment 2, plantarflexor MVC (47.1%), dorsiflexion ROM (14.7◦) and stretch tolerance (108%) increased significantly after training, while no change was found in MTU stiffness (passive moment at the same joint angle; 2.5%). A significant decrease in passive muscle stiffness (20.6%) but increase in tendon stiffness (27.7%) was observed. Discussion: A more than 2-fold greater acute increase in ROM was evoked after AMS than SS; the similar results in the second session (SS2 and AMS2) indicate that the finding is not due to muscle damage from unaccustomed training session. A stretch-induced muscle strength decrease was observed after SS but not AMS. After 6-week AMS training, substantial increases in ROM,strength, tendon stiffness and elastic energy storage, but reduction in muscle stiffness, demonstrate that AMS can provide significant physical function benefits whilst reducing risk of muscle injury

Isokinetic eccentric exercise substantially improves mobility, muscle strength and size, but not postural sway metrics in older adults, with limited regression observed following a detraining period

© 2020, The Author(s). Introduction: Eccentric exercise can reverse age-related decreases in muscle strength and mass; however, no data exist describing its effects on postural sway. As the ankle may be more important for postural sway than hip and knee joints, and with older adults prone to periods of inactivity, the effects of two 6-week seated isokinetic eccentric exercise programmes, and an 8-week detraining period, were examined in 27 older adults (67.1 ± 6.0 years). Methods: Neuromuscular parameters were measured before and after training and detraining periods with subjects assigned to ECC (twice-weekly eccentric-only hip and knee extensor contractions) or ECCPF (identical training with additional eccentric-only plantarflexor contractions) training programmes. Results: Significant (P \u3c 0.05) increases in mobility (decreased timed-up-and-go time [− 7.7 to − 12.0%]), eccentric strength (39.4–58.8%) and vastus lateralis thickness (9.8–9.9%) occurred after both training programmes, with low-to-moderate weekly rate of perceived exertion (3.3–4.5/10) reported. No significant change in any postural sway metric occurred after either training programme. After 8 weeks of detraining, mobility (− 8.2 to − 11.3%), eccentric strength (30.5–50.4%) and vastus lateralis thickness (6.1–7.1%) remained significantly greater than baseline in both groups. Conclusion: Despite improvements in functional mobility, muscle strength and size, lower-limb eccentric training targeting hip, knee and ankle extensor muscle groups was not sufficient to influence static balance. Nonetheless, as the beneficial functional and structural adaptations were largely maintained through an 8-week detraining period, these findings have important implications for clinical exercise prescription as the exercise modality, low perceived training intensity, and adaptive profile are well suited to the needs of older adults

Comparing maximal mean and critical speed and metabolic powers in elite and sub-elite soccer

The quantification of maximal mean speed (MMS), maximal mean metabolic power (MMP met), critical speed (CS) and critical metabolic power (CP met) was conducted over full A-League (elite) and National Premier League (NPL; sub-elite) seasons. Comparisons were made between levels of soccer competition and playing positions (i. e. centre backs, full backs, central midfielders, wide midfielders and strikers). A symmetric moving average algorithm was applied to the GPS raw data using specific time windows (i. e. 1, 5, 10, 60, 300 and 600 s) and maximal values were obtained. Additionally, these maximal values were used to derive estimates of CS and CP met. Maximal mean values, particularly during smaller time windows (i. e. 1 and 5 s), were greater in A-League match play. Only MMP met1 was identified as being consistently different between competitions (P = \u3c 0.001 – 0.049) in all playing positions. Significance was only observed in CS (P = 0.005) and CP met (P = 0.005) of centre backs between competitions. Centre backs were identified as the least energy demanding playing position. The present findings suggests that both maximal mean and critical analyses are suitable alternatives to common absolute distance and speed assessments of match running performance during competitive matches. © 2020 Georg Thieme Verlag KG StuttgartNew York

Estimates of persistent inward currents increase with the level of voluntary drive in low-threshold motor units of plantar flexor muscles

This study tested whether estimates of persistent inward currents (PICs) in the human plantar flexors would increase with the level of voluntary drive. High-density surface electromyograms were collected from soleus and gastrocnemius medialis of 21 participants (29.2 ± 2.6 yr) during ramp-shaped isometric contractions to 10%, 20%, and 30% (torque rise and decline of 2%/s and 30-s duration) of each participant’s maximal torque. Motor units identified in all the contraction intensities were included in the paired-motor unit analysis to calculate delta frequency (DF) and estimate the PICs. DF is the difference in discharge rate of the control unit at the time of recruitment and derecruitment of the test unit. Increases in PICs were observed from 10% to 20% [D = 0.6 pulse per second (pps); P < 0.001] and from 20% to 30% (D = 0.5 pps; P < 0.001) in soleus and from 10% to 20% (D = 1.2 pps; P < 0.001) but not from 20% to 30% (D = 0.09 pps; P = 0.724) in gastrocnemius medialis. Maximal discharge rate increased for soleus and gastrocnemius medialis from 10% to 20% [D = 1.75 pps (P < 0.001) and D = 2.43 pps (P < 0.001), respectively] and from 20% to 30% [D = 0.80 pps (P < 0.017) and D = 0.92 pps (P = 0.002), respectively]. The repeated-measures correlation identified associations between DF and increases in maximal discharge rate for soleus (r = 0.64; P < 0.001) and gastrocnemius medialis (r = 0.77; P < 0.001). An increase in voluntary drive tends to increase PIC strength, which has key implications for the control of force but also for comparisons between muscles or studies when relative force levels might be different. Increases in voluntary descending drive amplify PICs in humans and provide an important spinal mechanism for motor unit discharging, and thus force output modulation. NEW &amp; NOTEWORTHY Animal experiments and computational models have shown that motor neurons can amplify the synaptic input they receive via persistent inward currents. Here we show in humans that this amplification varies proportionally to the magnitude of the voluntary drive to the muscle.</p

Faster movement speed results in greater tendon strain during the loaded squat exercise

Introduction: Tendon dynamics influence movement performance and provides the stimulus for long-term tendon adaptation. As tendon strain increases with load magnitude and decreases with loading rate, changes in movement speed during exercise should influence tendon strain. Methods: Ten resistance-trained men [squat one repetition maximum (1RM) to body mass ratio: 1.65 ± 0.12] performed parallel-depth back squat lifts with 60% of 1RM load at three different speeds: slow fixed-tempo (TS: 2-s eccentric, 1-s pause, 2-s concentric), volitional-speed without a pause (VS) and maximum-speed jump (JS). In each condition joint kinetics, quadriceps tendon length (LT), patellar tendon force (FT) and rate of force development (RFDT) were estimated using integrated ultrasonography, motion-capture and force platform recordings. Results: Peak LT, FT, and RFDT were greater in JS than TS (p<0.05), however no differences were observed between VS and TS. Thus, moving at faster speeds resulted in both greater tendon stress and strain despite an increased RFDT, as would be predicted of an elastic, but not a viscous, structure. Temporal comparisons showed that LT was greater in TS than JS during the early eccentric phase (10-14% movement duration) where peak RFDT occurred, demonstrating that the tendon’s viscous properties predominated during initial eccentric loading. However, during the concentric phase (61-70% & 76-83% movement duration) differing FT and similar RFDT between conditions allowed for the tendon’s elastic properties to predominate such that peak tendon strain was greater in JS than TS. Conclusions: Based on our current understanding, there may be an additional mechanical stimulus for tendon adaptation when performing large range-of-motion isoinertial exercises at faster movement speeds

Greater strength gains after training with accentuated eccentric than traditional isoinertial loading loads in already strength-trained men

As training experience increases it becomes more challenging to induce further neuromuscular adaptation. Consequently, strength-trainers seek alternative training methods in order to further increase strength and muscle mass. One method is to utilize accentuated eccentric loading, which applies a greater external load during the eccentric phase of the lift as compared to the concentric phase. Based upon this practice, the purpose of this study was to determine the effects of 10 weeks of accentuated eccentric loading versus traditional isoinertial resistance training in strength-trained men. Young (22±3 y, 177±6 cm, 76±10 kg, n = 28) strength-trained men (2.6±2.2 y experience) were allocated to concentric-eccentric resistance training in the form of accentuated eccentric load (eccentric load = concentric load + 40%) or traditional resistance training, while the control group continued their normal unsupervised training program. Both intervention groups performed three sets of 6-RM (session 1) and three sets of 10-RM (session 2) bilateral leg press and unilateral knee extension exercises per week. Maximum force production was measured by unilateral isometric (110° knee angle) and isokinetic (concentric and eccentric 30°.s-1) knee extension tests, and work capacity was measured by a knee extension repetition-to-failure test. Muscle mass was assessed using panoramic ultrasound and dual-energy x-ray absorptiometry. Surface electromyogram amplitude normalized to maximum M-wave and the twitch interpolation technique were used to examine maximal muscle activation. After training, maximum isometric torque increased significantly more in the accentuated eccentric load group than control (18±10% vs. 1±5%, p<0.01), which was accompanied by an increase in voluntary activation (3.5±5%, p<0.05). Isokinetic eccentric torque increased significantly after accentuated eccentric load training only (10±9%, p<0.05), whereas concentric torque increased equally in both the accentuated eccentric load (10±9%, p<0.01) and traditional (9±6%, p<0.01) resistance training groups; however, the increase in the accentuated eccentric load group was significantly greater (p<0.05) than control (1±7%). Knee extension repetition-to-failure improved in the accentuated eccentric load group only (28%, p<0.05). Similar increases in muscle mass occurred in both intervention groups. In summary, accentuated eccentric load training led to greater increases in maximum force production, work capacity and muscle activation, but not muscle hypertrophy, in strength-trained individuals

Physical performance differences between weight-trained sprinters and weight trainers

The present study tested and compared well-trained athletes who were performing low-velocity, high-force resistance training and sprint running training (ST) when recruited, with subjects who were performing low-velocity, high-force resistance training but not sprint training (NST) when recruited. Eleven male sprint runners (mean ± SD; age = 19.0 ± 1.4 yr: height = 182.0 ± 4.7 cm: mass = 75.7 ± 4.7 kg), and eight male weight-trained athletes who were not currently performing sprint training, or any other additional training, (mean + SD; age = 21.5 ± 1.8 yr: height = 184.5 ± 3.6 cm: mass = 78.4 ± 4.6 kg) participated in the study; all subjects had a minimum of two years resistance training experience. Tests included 1. running speed (20 m time after a 50 m acceleration distance and 20 m acceleration time from a stationary start), 2. isokinetic hip flexor/extensor torque (and torque adjusted for body mass), angle of peak torque, time to reach peak torque and torque acceleration energy at low (1.05 rad.s−1 [60°.s−1]), moderate (4.74 rad.s−1 [270°.s−1]) and high (8.42 rad.s−1 [480°.s−1]) speeds and 3. maximum squat lift. ST subjects produced more isokinetic hip extensor torque when adjusted for body mass at 4.74 rad.s−1 (270°.s−1;