Nathan J. Porcher DCa, *; and Thomas J. Solecki DC, DACBSP, DACRBb
aPrivate Practice, Arlington Heights, IL
bAssistant Professor, National University of Health Sciecnes, Lombard, IL
*Corresponding Author. Nathan Porcher DC, 115 N. Arlington Heights Road, Suite 104, Arlington Heights, IL 60004. Email address: email@example.com (N. J. Porcher)
Running Head: Dynamic Warm-Up In The Workplace
Introduction: Virtually every company is looking for ways to make their employees safer, more effective, and protected from injury. The United States Bureau of Labor Statistics reports that hundreds of thousands of non-fatal injuries involving sprains, strains, tears, and back injuries affect the American workforce annually. While a push for pre-work stretching and designing of an ergonomic workstation have helped, an even greater decrease in work-related injuries could result from replacing static stretch routines with a dynamic warm-up, involving various, tailored exercises and proprioceptive tasks for employees to perform prior to the start of their work day.
Methods: We searched the terms, “dynamic warm-up,” on Pubmed. Our search was limited to human subjects, articles published within the last 10 years (August 2004- 2013), and published in English.
Results: The search yielded a total of 116 articles. We examined each article for relevancy, study design, and significance of findings, and selected to review pertinent articles that compared the efficacy of a dynamic warm-up (DWU) to models of static stretching (SS). Our findings demonstrate evidence that may support the use of dynamic warm-ups as a replacement to static stretching warm-ups.
Conclusion: Much evidence shows both the detriment of static stretching before athletic performance (strength, power, muscle efficiency) as well as the enhancement of performance by the use of a dynamic warm-up. This suggests that the occupational community, especially blue-collar-type jobs, could follow the athletic community in researching these interventions, in order to enhance work performance, to decrease work-related strain injuries, missed days of work, and workers’ compensation payouts by employers.
Key Words: Dynamic Stretching, Static Stretching, Workplace Injuries, Worker’s Compensation, Work-Related Injuries, Repetitive Strain Injury
Former student athletes who return to visit their alma mater’s sports team at practice or competition may be surprised to see coaches instructing athletes to prepare for competition in a way that is different than when they were on the team several years prior. It is really no surprise, however, that many coaches have greatly decreased the amount of static stretching (SS) and replaced much of it with a type of warm-up that much of the evidence in current literature may be pointing to as superior—dynamic warm-ups (DWU). Dynamic warm-ups and dynamic stretching, in contrast to static stretching, include active movements where muscles are taken through the full range of motion, and often include movement drills (i.e. light plyometrics, tri-planar exercises). A good coach wants to see his or her hard-working athletes performing to their highest potential, and of course, does not want to see them be sidelined for injuries that could have been prevented by using the most effective warm-up techniques. In the same way, every employer wants their employees, whom they have spent hours training, and who are the means of making their business function, be functioning at the highest level possible, and not absent from work due to injuries experienced on the job, and so a similar approach, using dynamic warm-up strategies for workers could potentially prove as beneficial.
“Repetitive strain injuries,” or RSIs, cause the average employee to miss 8 days of work each year, and the incidence of RSIs have soared by 30% in the last decade, according to a recent study, costing businesses over $600 million in workers’ compensation payout . Recently, the US Bureau of Labor Statistics published on their website that these types of sprain, strains and low back injuries have become a detriment to over 500,000 working individuals annually.
RSIs have been on the forefront of occupational injury discussions for the past 30 years and have a number of causative factors . Without providing too much detail, they are the result of a continuing cycle of cumulative trauma to the soft tissues over days, months, and years. The severity of insult to the tissues is a product of the number of repetitions by a muscle or tissue, the force of tension on that tissue, and is also dependent on the amplitude of each repetition (how much the muscle or tissue must lengthen and shorten, and whether or not significant rest is employed between repetitions) [17,22]. From a machinist, to an assembly line worker, to an electrician, and even to a keyboardist, all of these factors play a role. Because most individuals are de-conditioned and are not warming up properly, their muscle contractions require a higher percentage of muscle fiber recruitment in order to produce the needed amount of force to complete the task, thereby increasing the tension in the muscle and on the musculo-tendinous interface . Additionally, because many individuals are weak or are not properly warmed up, there is more overall load on the tissues and less of a chance for relaxation of these work-required muscles during the workday. The lack of both relaxation and relief of tension in a muscle prevents the proper amount of arterial and venous blood flow. Decreased blood flow leads to increased levels carbon dioxide and metabolic wastes lingering in these affected tissues. This results in chemotaxic stimulation of fibroblast cells, which lay down disorganized collagen fiber, essentially producing weak and non-compliant scar tissue, in and around muscles and the musculo-tendonous junctions. Because of the infiltration of scar tissue, the muscles and tendons thereby become weaker, less resilient, more sensitized to pain, and more likely to become re-injured, thus perpetuating the cycle . Because of this glaring issue, many employers have implemented programs such as pre-work static stretching, personal demands analysis (PDA), work task risk assessments, and ergonomic equipment into their workforce over the last couple of decades. These programs have helped somewhat to decrease these work-related sprain/strains, but the burden of dollars paid out annually by American companies with these interventions is clearly still astounding—this raises the question—are there still missing pieces in solving the puzzle of occupational RSI?
Perhaps, the idea of following the athletic community, and their research, implementing tailored dynamic warm-up routines for the occupational community, (and combining it with ergonomic advances already in place), could prove to be a key to cutting down on repetitive strain injuries, and therefore a company’s workers’ compensation payouts. In the previous 10 years, there have been a number of scholarly research articles published that demonstrate the benefits of a tailored, dynamic warm-up for the athletic population, in contrast to older static stretching routines, which are still in place in most occupational settings. The purpose of our study is to review the current literature for specific examples of how the realm of athletics has seen significant increases in performance measures and decreases in soft tissue injuries when utilizing dynamic warm-up routines, rather than static stretching alone. Our findings are intended to create a movement where research in the realm of the efficacy of DWU in the workplace is a better intervention than SS routines in increasing work performance and decreasing RSIs. The working public, whose responsibilities at work often require musculoskeletal efforts that in some ways correlate to the more complex efforts in sport-specific activities. While an athlete may be performing large scale global movements, the individual who lifts and loads boxes into a truck, a carpenter who moves heavy materials and applies forces through tools, or the assembly line worker who feeds sheet metal through a press for 8 hours each day have similar challenges to the muscles and other soft tissues. These findings could provide the groundwork for further research of how effective dynamic warm-up routines could positively affect a company’s workers’ compensation payouts, days of productivity lost, and therefore their annual overhead.
Our methods for this research included a search of scholarly articles on the topic in Pubmed. We used the terms, “dynamic warm-up,” in the subject line. In order to provide the best and most current evidence for our research, we limited our findings to articles published within the last 10 years (April 2004-April 2013). We also limited our search to studies involving human subjects, and chose to pursue only studies that were written in English. After we applied these filters, there was a yield of 116 articles. After this, we looked through all of the articles and selected those that were most pertinent to our study, comparing the efficacy of a dynamic warm-up to static stretching routines for athletes/employees to perform before beginning work. Before going any further, we examined each of the studies we selected for any bias that could have lead to significant alterations in their results. For this possible exclusion from our review, we ensured that the conclusions drawn from these studies matched the individual results from their research and had statistical significance, and that the studies were carried out in a professional manner with proper data collection. We also inspected data regarding project funding, if shown, to see if there may have been any conflict of interest that could potentially influence their conclusions or results. We are aware that, even in spite of our selection criteria, that there may have been articles published having similar data or results that were missed and were therefore not included in the study, but we felt that these studies reviewed below, as examples, were fair studies that adequately compared the efficacy of a dynamic warm-up routine to that of a static stretching warm-up. This narrative review of the literature regarding the efficacy of dynamic warm-up over static stretching, the benefits of dynamic warm-up, and the potential detriments of static stretching is designed to show that DWU-type routines may be superior to static stretching routines in the athletic population, and to suppose that the findings would translate well to the working population. Our research is intended to create a spark for research into whether or not replacing static stretching in the workplace with DWU routines is an effective way to create optimum performance, well-being, and most importantly, to lower repetitive strain injuries.
NARRATIVE SUMMARY OF SELECTED ARTICLES
The first study we selected was the most comprehensive overview of the contrast between dynamic and static stretching routines on performance. Behm and Chaouachi demonstrated, in a systematic review study, how static stretching has a negative effect in most cases . They examined 42 different studies, containing over 1600 participants who performed static stretching prior to performing activities that measured isokinetic force and torque, isokinetic power, and one-rep maximum performance activities, such as squats and bench presses. Of all the measures taken from the sum total of the 42 trials, there were over 50 measures that showed significant impairment brought on by static stretching before the activity, almost 20 that showed no change, and only 11 that showed improvement due to static stretching. They also examined 20 studies that had individuals performing vertical jump tests, countermovement jumps (moving in multiple planes), and squat jumps. Of these measures, 17 showed significant impairment on performance due to static stretching prior to testing, 7 showed no difference in performance, and 6 showed improvement. Most of these studies demonstrated moderate time spent stretching each muscle group of interest, from 90 seconds to 2 minutes each. Additionally, they cited previous work by Behm, et. al. , and Nagano et. al. , which demonstrated how static stretching could actually cause impairments in reaction time and balance. They also cited Power et. al. , which demonstrated impairment in muscle activation and maximal volumetric contractions for 2 hours post static stretching. To be fair and objective, as stated above, not all studies analyzed by Behm and Chaouachi were unanimous in detecting negative effects of static stretching prior to activity . Worrell, et. al. showed increase in hamstring torque following 15-20s stretches to the hamstrings . There were also several studies, as stated above, that showed that there was no statistically significant detriment to performance brought on by static stretching [26,30]. A few studies were mentioned where middle-aged participants were used. One study  showed no detriment to static stretching, but another was consistent with the majority of studies, showing negative effects on performance . Behm and Chaouachi’s review examined the acute effects of a dynamic warm-up. While there were a much wider variety of types of dynamic stretching (i.e. taking the muscle carefully through full range of motion, plyometric exercises), they demonstrated in many papers that there were benefits on subsequent performance . Some articles they reviewed showed dynamic warm-ups to have no effect, but no studies provided examples of any negative effects. At times, these studies used movements that simulated parts of the total upcoming performance motion. Their research also showed that longer periods of dynamic stretching (the day of, as well as implementation over days or weeks) were more likely to produce significant positive effects on performance. The authors stated that further research was needed in the realm of dynamic warm-ups.
The second study we examined was a very recent e-publication from the Journal of Strength and Conditioning Research by Haddad et. al. Their study selected 16 junior soccer players between the ages of 17 and 19. They chose to use the five jump test (5JT), repeated sprint ability test (RSA), and 30 meter sprints (with 10 and 20 meter splits)—tests which have been designed to measure lower body efficiency and explosiveness. Each of the 16 individuals was taught how to stretch statically and dynamically, and were familiarized with what to do for the “control” group setting. Each player performed testing at the 2nd and 4th week of pre-season training sessions, 24 hours after each of the different stretch protocols. Protocols were tested on separate days, not together. The athletes did not use either stretching protocol after a basic warm-up the morning of the testing. The results of the study demonstrated that statistically significant inhibition of lower body efficiency and explosiveness was a result of static stretching, even 24 hours prior to the test, as seen in the 5JT and 30m sprint. The repeated sprint ability was not affected significantly by static stretching 24 hours prior to testing .
The next study we chose to examine more closely regarding the benefits of a dynamic warm-up (DWU) in contrast to a static stretching warm-up (SWU) was from the Journal of Strength and Conditioning Research in 2012. Aguilar et. al. had 45 healthy male and female individuals from recreational soccer teams participate in the study. The study looked at the measures of large muscle group flexibility, concentric and eccentric strength of these muscle groups, and vertical jump performance. All participants were pre-tested and then randomized into DWU, SWU, and control (CON) groups. All groups began with a 5-minute aerobic warm-up on a stationary bike. The DWU group performed a plethora of active movements such as dynamic stretching, plyometrics, running, and dynamic stretching containing a proprioceptive (balance) requirement. SWU performed 10 minutes of static stretching on the muscle groups of interest, and the control group sat resting for the 10-minute duration. Following those three separate 15-minute warm-up interventions, participants were re-tested. The DWU group showed significant increase in hamstring flexibility, as well as in peak quadriceps torque in both concentric and eccentric types of contraction from pre-test to post-test. The SWU group had findings indicating that the optimum hamstring to quadriceps strength ratio may have even been upset by prolonged static stretch duration .
Another very helpful study in this realm of dynamic warm-ups was written by Daneshjoo et. al. and published in the PLOS One Journal in December 2012. This study examined very different measures from those above regarding the efficacy of a dynamic warm-up on proprioception and both static and dynamic balance. Thirty- six participants from professional soccer teams were randomized into three groups. Two of these groups used one of two pre-written dynamic warm-up routines (FIFA 11+ and HarmoKnee), and the third group acted as a control and were not instructed to warm up in any specific way, but were told to warm up according to their normal routine. Unlike other studies, these dynamic interventions were performed for 24 sessions ( over a period of 2 months) between pre-testing and post-testing. Some of the dynamic warm-ups performed daily by these individuals included planks, side planks, single leg balance with a medicine ball, vertical jumps, bounding, walking lunges, hamstring curls against resistance, and glute bridging. The testing measures included having patients standing on a Biodex Isokinetic Dynometer (essentially measuring change in center of pressure) with their knee flexed at 30, 45, and 60 degrees over 3 different trials. Dynamic postural control was assessed via the Star Excursion Balance Test, having subjects reach in 8 different directions. Individuals were to touch their non-dominant foot to the star-patterned floor tape in each direction as far as possible from the center. Leg length was standardized for each individual and factored into their tests. Further distances reached indicated greater dynamic balance, and tests were discarded and repeated when test subjects either lost their balance or moved their stance foot from the center of the star. Lastly, a standard Single Leg Stance (SLS) test was administered with the individuals’ hands on their hips. Data were collected for both eyes-open and eyes-closed trials, and all subjects were timed from the moment they lifted their leg to the point at which they put their leg down, broke stance, or removed their hands from their hips. Each individual was allowed to have three trials in the SLS test. Results of the dynamic warm-up programs both significantly decreased proprioceptive error at 45 and 60 degrees of knee flexion. For the 11+ and HarmoKnee groups, dynamic balance increased by 12.4% and 17.6%, respectively. Additionally, static balance also increased with eyes open 10.9% and 6.1%, respectively; and testing with eyes closed increased by 12.4% and 17.6%, respectively, over the course of 2 months .
In late 2009, there was another article in the Journal of Strength and Conditioning Research, by Curry et. al., showing the effects of dynamic stretching, static stretching, and light aerobic activity on muscular performance. Twenty-four active, but untrained women in their mid-twenties were recruited for the study. The first aspect of the study looked at potential intervention-driven changes in quadriceps length as measured by passive knee flexion in Modified Thomas position using goniometry. Counter-movement jump (CMJ) performance was also measured pre- and post-testing, as was the time to peak force of the quadriceps muscle (at 90 degrees of knee flexion), which was tested using KinCom isokinetic dynometer. All participants were familiarized with each type of warm-up intervention, but they were not told the names of each intervention. All administers of the testing measures were blinded to the type of warm-up that each subject had performed prior to testing. Each outcome measure was pre-tested on each individual after 5 minutes on a stationary bike. After this, 15 minute cycles of each intervention were administered in separate sessions to the same subjects. Post-warm up testing was performed at 5 minutes, and 30 minutes to show the lasting effects of each warm-up intervention. All three techniques showed improvement in muscle length, which decreased in all three from 5 minutes to 30 minutes. CMJ performance increased significantly with light aerobic activity and dynamic stretching at 5 minutes, and static stretching was shown to cause significant detriment. After another 25 minutes of sitting at rest, all three intervention groups were lower than at their pre-test results. Time to peak force (TPF) had decreased significantly after dynamic stretching, and continued to stay at a significantly faster time than pre-testing even 30 minutes after the dynamic stretching and movements had been executed. Both static stretching and light aerobic warm-up interventions showed little change in Time to Peak Force (TPF) at 5 minutes, and TPF was actually longer than the baseline times at 30 minutes post-intervention .
Herman et. al. also demonstrated the effects of a repeated, tailored dynamic warm-up routine, as compared to the effects of static stretching and on a number of different measures in 24 Division I collegiate wrestlers. Their dynamic warm-up intervention consisted of both movement drills and calisthenics, and the static stretch group instead performed 8 stretches during the allotted time. These groups performed their respective warm-up routines 5 times per week for 4 weeks. The performance measures used were a standing broad jump, medicine ball toss, peak torque of quadriceps muscle, sit-ups, push-ups, 300m, and 600m runs. In each test, the dynamic warm-up positively influenced the results, whereas the static-stretching warm-up did not cause any improvement. Furthermore, the push-up tests and 600m run outcomes decreased significantly, on average, among the static stretching group .
There were a few other studies that showed that a dynamic warm-up following static stretching could potentially “redeem” the upcoming performance that would have otherwise been inhibited due to the properties of muscle affected by a static stretch . One of the more straightforward studies was done by Morrin and Redding, for the Journal of Dance Medicine and Science, in early 2013, although there have been other studies implicated in having similar findings [28,29]. They selected 10 experienced dancers that would visit 4 different locations, to perform 4 different types of warm-ups (static only, dynamic only, combined, and control—no warm-up). They were then tested for ROM of the muscle groups stretched, vertical jump, and balance (measuring ellipse area of center of gravity shifts on balance platform.) Dynamic stretching gave the least amount improvement in ROM, but the combination of both types of stretching techniques produced nearly equal results to the positive ROM change observed in the static stretch trial. Average vertical jump heights and balance were statistically better for the dynamic warm-up group than the static stretch group, and also generally better than the combination group.
It has become fairly common knowledge to the American public that specific warm-ups increase blood flow and raises temperature in the body parts that will be used more strenuously in the subsequent workload [27,6]. To a exercise physiologist, sports physician, or athletic trainer, it is known that proper warm-ups also speed up nerve impulses, decrease muscle viscosity, increase muscle post- activation potentiation (greater response and speed of contraction for added power and strength), increase proprioception, and ultimately lead to safer, peak performance. Unfortunately, this knowledge is almost always placed under the category of athletic performance and seldom thought of in the realm of occupational performance. Athletes in various sports tend to perform global, whole body movements, using complex muscle coordination to accomplish the task that their sport requires. However, just as an athlete must execute specific skills or movements, requiring force development in order to compete and practice their disciplines, individuals who perform some jobs, especially, but not limited to those with heavier-duty work, require similar amounts of force production, torque, and dynamic activity. From the rugby player, to the competitive weight lifter, to the concrete cutting contractor, and to the steel worker, the same muscle tissues must produce specific forces for a sustained period of time. Because of this often-overlooked association, America’s workforce is likely missing out on what the current literature deems to be the best type of pre-work routines to prevent injuries and maximize performance.
It is common knowledge that static stretching programs and ergonomic interventions in the workplace have been implemented in recent past, but it seems that very few, if any companies, are following how the current literature is weighing out static stretching versus a dynamic warm-up, and experimenting with additions of DWU protocols to their employees’ daily warm-ups. By looking at the best of the recent studies regarding the benefits of dynamic warm-up strategies for athletes, we can surmise that a similar effect would be generated when applied to the occupational workforce.
In a majority of the articles discussed above, it is demonstrated that a stand-alone static stretching protocol may not only be inferior to dynamic warm-up routines, but may be an actual hindrance to performance of an athlete, and therefore a factory worker, carpenter, or any other profession requiring force and dynamic activity. Behm and Chaoachi’s paper brought in a number of sources showing the detrimental effects of static stretching on performance, as well as the potential benefits of dynamic stretching . What’s more, compelling evidence from Haddad, et. al., demonstrated that this deleterious effect may last as long as 24 hours . Competitive athletes and the working public all have the same muscles and tissues, but something to consider as we relate the two groups is that much of the American workforce is de-conditioned to some degree. Because of being in a de-trained state, it is possible that static stretching programs would have even greater negative effects on them as they entered their workday. Egan et. al. and Unick et. al. in 2006, and 2005, respectively, demonstrated that untrained subjects saw a more deleterious effect on performance following static stretching routines [11,31]. This was likely due to the fact that trained individuals had a more pliable musculo- tendinous junction that could tolerate the visco-elastic changes in the muscles following their bouts of static stretching. Aguilar et. al. showed that a dynamic warm-up routine contributes to proper muscle strength and flexibility ratios of the hamstring and quadriceps muscles, which in turn enhanced performance and likely protected the surrounding joints influenced by those muscles from wear and tear . The interplay of the hamstrings and quadriceps working properly around a joint can be related to most other agonist-antagonist muscle relationships in the body. Daneshjoo et. al. showed significant positive effects on proprioception, static and dynamic balance when individuals followed a specified, tailored dynamic warm-up routine for 8 weeks. These authors also commented in their discussion that in order to improve the dynamic warm-up measures, further core exercise implementation should be added for greater stabilization effect. Herman and colleagues’ work also demonstrated that a DWU routine implemented over a longer period of time can have positive effects on muscle strength, power, endurance, agility, and flexibility . Curry et. al. mentioned that even in untrained individuals, that dynamic stretching had not only an immediate effect on time to peak torque of a muscle (a measure that essentially demonstrates the effective strength of that muscle), but also had a lasting effect that would likely be perpetuated by continued occupational or athletic activity . Morrin et. al. also demonstrated improved proprioception due to a dynamic stretching or combined dynamic and static stretching . Many past studies have demonstrated how individuals suffering from low back pain were much more likely to have proprioceptive deficits both sitting and standing than those individuals who did not [24,25,32,33]. Since a great number of individuals in America’s workforce experience low back pain on a daily basis, any measure of increasing proprioception, by different dynamic strategies would be likely be welcomed.
We realize that there are a number of limitations to our research. We did not perform a systematic review of the literature; thus, the articles we selected to review and summarize were intended to stir up a desire for others to research the subject, not make any assumptions about the efficacy of dynamic warm-up routines in the work place. Despite our intentions, we realize that there is potential for author bias. Unfortunately, there is not yet any published research that we are aware of that compares and contrasts DWU and SS routines in the workplace, and so our research is aimed at the athletic realm, where these two types of warm-ups have been thoroughly studied. Yet, again, our research intends to steer an interest for research in that direction, not provide a definitive answer as to which is better. We also acknowledge that our search methods may have missed some pertinent studies.
FUTURE SUGGESTIONS FOR RESEARCH:
We suggest that, based on what has been found in the literature by many studies, like ours, that future research should look at the potential benefits of DWU over SS routines, or a combination of both in the workplace using outcome measures of work performance, discomfort/pain experienced while on the job, documented soft-tissue injuries, and the like, which could prove useful for employees, as well as their employers.
With these studies mentioned above, as well as a great number of other studies, it is clear that there may be a real benefit to either adding a DWU routine to stretching, or even replacing the SS altogether with a DWU in the athletic population. Based on the physiological effects happening with these two types of warm-up routines, this conclusion could perhaps be true for the working population, as well, although further research is needed, as we have stated above to investigate the effects in that setting. Still, it is worth noting that while static stretching may cause acute and somewhat lasting detrimental changes in overall muscle performance, should not be avoided altogether, because of the several studies that demonstrate that static stretching at the end of the day in order to gain back muscle length, or in situations where the acute effects of it will not alter performance [2,18]. It still does have benefits of increasing range of motion, muscle length (especially at the musculo-tendinous interface) . It also will, over time, make the tissue more compliant and less stiff for the intended movements . This is especially true in middle-aged populations, where there is a likelihood of workers having lived in a de-conditioned state for a longer duration of time and having a greater degree of muscle-tendon unit stiffness. Perhaps, if these results were translated to the workplace, employers could use DWU routines before work, but still suggest that their workers use static stretching after a work day, or on days off. Still, it may be judicious, according to the preponderance of the evidence, to avoid static stretching protocols prior to performance, such as beginning an 8-hour day of hauling equipment around, or performing tasks associated with road construction . Workplace injuries, including sprains, strains, and low back injuries, keep an average employee out of work for 8 days each year, and cost employers hundreds of millions of dollars each year in workers compensation and other costs associated with losing man-hours, and even spill over into the private/group healthcare burden . We feel that is it time for those in research, and company ownership/management to begin to look at the weight of the evidence in the literature regarding better warm-up methods, and begin to study and learn how to implement these measures into the daily practice of their employees before they embark on a full day’s work. The benefits may lead to a happier staff, safer workplace, and may end up saving millions of dollars in unneeded workers’ compensation payouts.
FUNDING SOURCES AND POTENTIAL CONFLICTS OF INTEREST:
No funding sources or conflicts of interest were reported for this study.
The authors thank the Interlibrary Loan Department from the National University of Health Sciences’ Learning Resource Center for their assistance with obtaining full-text journal articles for the review.
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