Canadian Society For Exercise Physiology Position Stand on the Acute Effects of Muscle Stretching on Physical Performance, Range of Motion and Injury Incidence in Healthy Active Individuals

Muscle stretching in some form appears to be of greater benefit than cost (in terms of performance, ROM and injury outcomes) but the type of stretching chosen and the make-up of the stretch routine will depend on the context within which it is used. SS and PNF stretching are not recommended if prolonged (>60s total per individual muscle) stretching is employed within 5 min of an activity without subsequent dynamic activity (e.g. if prolonged stretching immediately precedes training or competition), unless the requirements for increases in ROM and/or decrease in (specifically) muscle injury outweigh the requirement for optimum physical performance. Injury reduction appears to require more than 5 min of total stretching of multiple task-related muscle groups. However, when an optimal pre-event warm-up with an appropriate duration of stretching is completed (i.e. initial aerobic activity, stretching component, task- or activity-specific dynamic activities) the benefits of SS and PNF stretching for increasing ROM and reducing muscle injury risk at least balance, or may outweigh, any possible cost of performance decrements. SS also appears to enhance performance in activities performed at long muscle lengths. DS may induce moderate performance enhancements and may be included in the stretching component to provide task-specific ROM increases and facilitation of dynamic SSC performance when performed soon before an activity, and/or when a full pre-activity routine is not completed; however there is no evidence as to whether it influences injury risk. Furthermore, while the literature examining the effect of stretching on physical performance is extensive, the literature examining injury risk is much smaller, and thus more research needs to investigate the effect of muscle stretching on injury risk

The effect of isokinetic dynamometer deceleration phase on maximum ankle joint range of motion and plantar flexor mechanical properties tested at different angular velocities

During range of motion (max-ROM) tests performed on an isokinetic dynamometer, the mechanical delay between the button press (by the participant to signal their max-ROM) and the stopping of joint rotation resulting from system inertia induces errors in both max-ROM and maximum passive joint moment. The present study aimed to quantify these errors by comparing data when max-ROM was obtained from the joint position data, as usual (max-ROMPOS), to data where max-ROM was defined as the first point of dynamometer arm deceleration (max-ROMACC). Fifteen participants performed isokinetic ankle joint max-ROM tests at 5, 30 and 60°·s-1. Max-ROM, peak passive joint moment, end range musculo-articular (MAC) stiffness and area under the joint moment-position curve were calculated. Greater max-ROM was observed in max-ROMPOS than max-ROMACC (P < 0.01) at 5 (0.2 ± 0.15%), 30 (1.8 ± 1.0%) and 60°·s-1 (5.9 ± 2.3%), with the greatest error at the fastest velocity. Peak passive moment was greater and end-range MAC stiffness lower in max-ROMPOS than in max-ROMACC only at 60°·s-1 (P < 0.01), whilst greater elastic energy storage was found at all velocities. Max-ROM and peak passive moment are affected by the delay between button press and eventual stopping of joint rotation in an angular velocity-dependent manner. This affects other variables calculated from the data. When high data accuracy is required, especially at fast joint rotation velocities (≥30°·s-1), max-ROM (and associated measures calculated from joint moment data) should be taken at the point of first change in acceleration rather than at the dynamometer’s ultimate joint position

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

Effects of acute and chronic stretching on pain control

ABSTRACT While muscle stretching has been commonly used to alleviate pain, reports of its effectiveness are conflicting. The objective of this review is to investigate the acute and chronic effects of stretching on pain, including delayed onset muscle soreness. The few studies implementing acute stretching protocols have reported small to large magnitude decreases in quadriceps and anterior knee pain as well as reductions in headache pain. Chronic stretching programs have demonstrated more consistent reductions in pain from a wide variety of joints and muscles, which has been ascribed to an increased sensory (pain) tolerance. Other mechanisms underlying acute and chronic pain reduction have been proposed to be related to gate control theory, diffuse noxious inhibitory control, myofascial meridians, and reflex-induced increases in parasympathetic nervous activity. By contrast, the acute effects of stretching on delayed onset muscle soreness are conflicting. Reports of stretch-induced reductions in delayed onset muscle soreness may be attributed to increased pain tolerance or alterations in the muscle's parallel elastic component or extracellular matrix properties providing protection against tissue damage. Further research evaluating the effect of various stretching protocols on different pain modalities is needed to clarify conflicts within the literature

Reliability of isokinetic tests of velocity- and contraction intensity-dependent plantar flexor mechanical properties

“Flexibility” tests are traditionally performed voluntarily relaxed by rotating a joint slowly; however, functional activities are performed rapidly with voluntary/reflexive muscle activity. Here, we describe the reliabilities and differences in maximum ankle range of motion (ROMmax) and plantar flexor mechanical properties at several velocities and levels of voluntary force from a new test protocol on a commercially available dynamometer. Fifteen participants had their ankle joint dorsiflexed at 5, 30, and 60° s−1 in two conditions: voluntarily relaxed and while producing 40% and 60% of maximal eccentric torque. Commonly reported variables describing ROMmax and resistance to stretch were subsequently calculated from torque and angle data. Absolute (coefficient of variation (CV%) and typical error) and relative (ICC2,1) reliabilities were determined across two testing days (≥72 h). ROMmax relative reliability was good in voluntarily relaxed tests at 30 and 60° s−1 and moderate at 5° s−1, despite CVs ≤ 10% for all velocities. Tests performed with voluntary muscle activity were only reliable when performed at 5° s−1, and ROMmax reliability was moderate and CV ≤ 8%. For most variables, the rank order of participants differed between the slow‐velocity, relaxed test, and those performed at faster speeds or with voluntary activation, indicating different information. A person's flexibility status during voluntarily relaxed fast or active stretches tended to differ from their status in the traditional voluntarily relaxed, slow‐velocity test. Thus, “flexibility” tests should be completed under conditions of different stretch velocity and levels of muscle force production, and clinicians and researchers should consider the slightly larger between‐day variability from slow‐velocity voluntarily relaxed tests

Mechanisms Underlying Performance Impairments Following Prolonged Static Stretching Without a Comprehensive Warm-up

Whereas a variety of pre-exercise activities have been incorporated as part of a “warm-up” prior to work, combat, and athletic activities for millennia, the inclusion of static stretching (SS) within a warm-up has lost favour in the last 25 years. Research emphasised the possibility of SS-induced impairments in subsequent performance following prolonged stretching without proper dynamic warm-up activities. Proposed mechanisms underlying stretch-induced deficits include both neural (i.e. decreased voluntary activation, persistent inward current effects on motoneurone excitability) and morphological (i.e. changes in the force-length relationship, decreased Ca2+ sensitivity, alterations in parallel elastic component) factors. Psychological influences such as a mental energy deficit and nocebo effects could also adversely affect performance. However, significant practical limitations exist within published studies, e.g. long stretching durations, stretching exercises with little task specificity, lack of warm-up before/after stretching, testing performed immediately after stretch completion, and risk of investigator and participant bias. Recent research indicates that appropriate durations of static stretching performed within a full warm-up (i.e. aerobic activities before and task-specific dynamic stretching and intense physical activities after SS) have trivial effects on subsequent performance with some evidence of improved force output at longer muscle lengths. For conditions in which muscular force production is compromised by stretching, knowledge of the underlying mechanisms would aid development of mitigation strategies. However, these mechanisms are yet to be perfectly defined. More information is needed to better understand both the warm-up components and mechanisms that contribute to performance enhancements or impairments when SS is incorporated within a pre-activity warm-up

Expectation of pain intensity does not influence neuromuscular performance but does influence pain perception during a maximal isometric knee extension task

Background: Experimentally induced pain can decrease maximal muscular force (Ervilha et al., 2004: Exp Brain Res, 156, 174-182) with reductions in muscular force and motor unit firing rate related to perceived pain intensity when pain is induced either invasively via hypertonic saline injections (Farina et al., 2005: Clin Neurophysiol, 116, 1558-1565) or from a non-invasive gross pressure device (GPD) (Wing et al., 2011: The severity of experimentally induced pain influences muscular performance during maximal voluntary isometric knee extensor contractions, 16th Annual Congress of the ECSS, Liverpool, United Kingdom). Purpose: The aim of the present study was to examine whether varying expectation of pain intensity influenced pain perception and neuromuscular performance during an isometric knee extensor task. Methods: Twenty-nine healthy male participants (mean; age = 22.8 ± 5.5 yr, height = 1.7 ± 0.2 m, mass = 84.1 ± 19.2 kg) volunteered for the study after giving written, informed consent following institutional ethical approval. Isometric knee extensor joint moment, electromyographic (EMG) activity of the vastus lateralis and semitendinosus muscles, and perception of pain intensity using a visual analogue scale (VAS) were measured during maximal voluntary isometric contractions during three experimental conditions. After pain perception threshold was determined, the participants were advised to expect 100%, 200% and 300% of pain perception threshold; however in all three conditions 200% of pain perception threshold was induced using a GPD. Repeated measures ANOVAs were used to investigate differences in VAS, joint moment and EMG activity between conditions. Significance was accepted at

The Evidence Base for Interventions Delivered to Children in Primary Care: An Overview of Cochrane Systematic Reviews

Background: As a first step in developing a framework to evaluate and improve the quality of care of children in primary care there is a need to identify the evidence base underpinning interventions relevant to child health. Our objective was to identify all Cochrane systematic reviews relevant to the management of childhood conditions in primary care and to assess the extent to which Cochrane reviews reflect the burden of childhood illness presenting in primary care.Methodology/Principal Findings: We used the Cochrane Child Health Field register of child-relevant systematic reviews to complete an overview of Cochrane reviews related to the management of children in primary care. We compared the proportion of systematic reviews with the proportion of consultations in Australia, US, Dutch and UK general practice in children. We identified 396 relevant systematic reviews; 385 included primary studies on children while 251 undertook a meta-analysis. Most reviews (n=218, 55%) focused on chronic conditions and over half (n=216, 57%) evaluated drug interventions. Since 2000, the percentage of pediatric primary care relevant reviews only increased by 2% (7% to 9%) compared to 18% (10% to 28%) in all child relevant reviews. Almost a quarter of reviews (n=78, 23%) were published on asthma treatments which only account for 3-5% of consultations. Conversely, 15-23% of consultations are due to skin conditions yet they represent only 7% (n=23) of reviews.Conclusions/Significance: Although Cochrane systematic reviews focus on clinical trials and do not provide a comprehensive picture of the evidence base underpinning the management of children in primary care, the mismatch between the focus of the published research and the focus of clinical activity is striking. Clinical trials are an important component of the evidence based and the lack of trial evidence to demonstrate intervention effectiveness in substantial areas of primary care for children should be addressed.</p