Tag Archives: Exercise Performance

Using NIRS to non-invasively monitor muscle oxygenation during exercise

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Skeletal muscles are the basis of all movement in the human body, and athletes work years to train their muscles to be powerful yet efficient. Even if a single muscle could allow a person to lift a car, it would not be very useful if the muscle could no longer create forceful contraction again for several hours. The muscle also must be efficient in the use of oxygen, ions, and other substrates that allow for contraction to be able to quickly recover and be prepared for repeated contraction. Muscle oxygenation is particularly important for both endurance and power of a muscle because it is necessary to produce ATP to power muscle cells to contract. Heart rate and blood oxygen delivery are helpful for getting an idea of an athlete’s efficiency, but they do not tell the whole story for the muscle. At the muscle, the balance between delivery and consumption of oxygen explains its efficiency [1]. To measure muscle oxygen saturation, a technique called near-infrared spectroscopy (NIRS) is used to get real time data to inform athletes of the state of their muscles during training. This is a powerful tool for maximizing athletic gains in muscles from training and to see the state of the muscle over time and after rest.

Early NIRS instrumentation was contained to the lab, but recently portable versions have become more common, which is very important for its use in both the medical and research fields. In medicine, NIR has been used for study of septic shock, free tissue transfer, real-time tissue perfusion during surgery, cancer nanotechnology, and peripheral arterial disease.  For this post, the use of NIR in exercise will be highlighted. In exercise, NIRS is a great tool because it is a non-invasive method that can be applied locally to muscles or tissues of interest and provide real time data during exercise. NIRS is highly sensitive to changes in muscle tissue oxygenation [2, 3, 4], and it reflects the balance between oxygen delivery and utilization, unlike measurements of arterial or venous blood samples which have been used previously and are minimally invasive [2]. NIRS works by measuring the percentage of oxygenated hemoglobin to total hemoglobin (oxygenated and deoxygenated hemoglobin) to give muscle oxygenation. Hemoglobin is the main oxygen carrying protein in the blood and can carry 4 oxygen molecules (O2). Oxygenated and deoxygenated hemoglobin scatter NIR light (600-1000 nm) differently, so their relative concentrations can be found from their molecular absorption coefficients. To do this, three to four different wave lengths of light will be used to determine the concentrations of each based on the change in molecular absorption coefficients at different wavelengths (Fig 1). NIR light must be used as it: 1) passes through skin, bone, and most biological tissue, and 2) is the appropriate wavelength where the small amount of absorption that occurs is predominately from hemoglobin (Fig 2) [5].  As the muscle performs work, the muscle oxygenation will decrease as a function of the work and the training of the muscle.

Fig. 1: Molecular Absorption Coefficient Profiles for Oxygenated and Deoxygenated Hemoglobin [5]

Fig 2: Light Absorption by Wavelength [5]

 

 

 

 

 

 

 

 

 

 

A patent on google patent claims to leverage this technology in a wearable article of clothing for athletes to be able to measure muscle oxygenation real-time (Fig 3) [6]. The patent claims to be a method and apparatus for assessing tissue oxygenation saturation through two main claims that summarize to: a portable apparatus that is a wearable article capable of measuring oxygenation saturation of at least one of a skin dermis layer, adipose layer, or muscular fascial layer of a user during physical activity using at least one near-infrared spectroscopy probe including at least one near-infrared light source and at least one photodetector. In short, the patent is a claim on a portable, wearable NIRS device for tissue oxygenation levels. NIRS has been a research method for decades, so the novel part of this patent lies in the incorporation of this technology into a wearable article of clothing.

Fig 3: Figure from patent illustrating wearable shirt, shorts, and socks using NIRS

Fig4: Figures from patent showing example data of muscle oxygenation average during constant rate running at different grades (top) and real time data from medial gastrocnemius muscle during weighted exercise and unweighted control (bottom)

This patent pertains primarily to the measurement of tissue during exercise (Fig 4). This could be of use for athletes during training to be able to compare what levels of exercise cause certain levels of muscle oxygen saturation loss. For example, highly trained athletes often train at high altitude to reduce oxygen in the air so that their body adapts to becoming more efficient with oxygen usage. This prompts higher performance when returning to normal oxygen levels. Using NIRS could allow them to find a training regime that caused the same hypoxia in muscle without traveling to higher altitude (they will still miss out on some of the pulmonary and cardio vascular advantages that training at altitude can produce). This may also be helpful in rehabilitation as the change in muscle oxygenation is an indicator that the muscle is being used and can inform physical therapists if the patient is engaging the correct muscles during rehab. Additionally, the device may also have merit in the medical realm for monitor muscle oxygenation in patients with chronic heart failure, peripheral vascular disease, chronic obstructive pulmonary disease, and varying muscle diseases [3, 4].

  1. Patent title: Method and apparatus for assessing tissue oxygenation saturation
  2. Patent number: US20170273609A1
  3. Patent filing date: 2017-03-22
  4. Patent issue date: Patent Pending
  5. How long it took for this patent to issue: TBD
  6. Inventor(s): Luke G. Gutwein, Clinton D. Bahler, Anthony S. Kaleth
  7. Assignee (if applicable): Indiana University Research and Technology Corp
  8. U.S. classification: A61B5/0075
  9. How many claims: 20

References and Further Reading

[1] BSX Athletics https://support.bsxinsight.com/hc/en-us/articles/204468695-What-is-muscle-oxygenation-

[2] Bhambhani, Y. N. (2004). Muscle Oxygenation Trends During Dynamic Exercise Measured by Near Infrared Spectroscopy. Can. J. Appl. Physiol., 29(4), 504–523.

[3] Hamaoka, T., Mccully, K. K., Quarisma, V., Yamamoto, K., & Chance, B. (2007). Near-infrared spectroscopy / imaging for monitoring muscle oxygenation and oxidative metabolism. Jounal of Biomedical Optics, 12(6), 1–16. http://doi.org/10.1117/1.2805437

[4] Boushel, R., & Piantadosi, C. A. (2000). Near-infrared spectroscopy for monitoring muscle oxygenation. Acta Physiol Scand, 168, 615–622. http://doi.org/10.1046/j.1365-201x.2000.00713.x

[5] Shimadzu Commercial Website https://www.ssi.shimadzu.com/products/imaging/labnirs-principle-of-operation.html

[6] Patent https://patents.google.com/patent/US20170273609A1/en?oq=US20170273609A1

[7] Ferrari, M., Muthalib, Makii, & Quarisma, V. (2011). The use of near-infrared spectroscopy in understanding skeletal muscle physiology : Phil. Trans. R. Soc. A, 369, 4577–4590. http://doi.org/10.1098/rsta.2011.0230 

[8] Artinis Commercial Site https://www.artinis.com/portamon#portamon-software

Is chronic stretching actually beneficial?

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Jackie Haffey and Matt Ballman

 

Have you ever wondered why stretching was always emphasized so heavily in gym classes growing up? Stretching is something that has been coupled with exercise all of our lives. Growing up we are taught to stretch before and after exercise in order to help prevent injury, promote recovery, and enhance your overall performance, but does it actually work? There are professional athletes out there who undergo strict training regimens that involve lots of stretching, but still manage to have career altering injuries like tearing their ACL. There are many athletes who are out there that are very talented but almost never stretch before or after a workout. On the flipside, there are many professional athletes out there that vow that stretching helps them extend their careers and improve recovery. In the NBA, yoga has become a common practice among players doing all that they can in order to help their bodies sustain their elite level of play and handle the rigors of playing in an 82 game season. Arguably the best player of all time Lebron James practices yoga regularly [6]. He even attributes it to helping him extend his career and play at a high level for as long as he has [6]. So does stretching actually help people perform better or avoid injury or is it all just a myth?

Figure1. Passive hamstring stretches

For a long time, stretching was highly recommended with little evidence to support it. Now studies are showing that acute stretching before exercise can actually be harmful as discussed in the previous blog post, “Holding Your Stretch is Holding You Back”.  So what is evidence saying about chronic stretching?When discussing effects of chronic stretching, it is referring to long term effects of consistent stretching. People normally associate this with increasing flexibility, or joint range of motion (ROM). The American College of Sports Medicine (ACSM) has recommendations for maintaining flexibility. A study was done in 2010 to support the ACSMs advice specifically for hip flexion [5]. There was a significant improvement in ROM for all stretching groups and a decrease for the control group [5]. The paper did mention its own limitation in only studying one muscle group, saying its findings should not be generalized to any muscles in the body. Another limitation was that the participants could not start a new or increase intensity of an existing exercise program during the study [5]. This may have allowed the collected data to have less noise but it may not accurately translate to real world scenarios as many athletes aim to increase workout intensity or switch up their workout programs. So with the knowledge that chronic stretching can increase ROM, how does it affect performance?

Table 1. Data from the 2007 study showing the improvements of the stretching group.

Table 2. Data from a study on D3 athletes showing no difference between stretching and control groups.

 

A study completed in 2007 had the goal of determining the effects of chronic stretching on specific exercise performances. Performed on relatively inactive people, the study lasted eight weeks long and tested whether stretching had an impact on power, strength, and endurance in the lower body by using various exercises according to each fitness category [1]. The, “stretching,” or experimental group showed significant improvement in all categories whereas the control group showed no improvements [1]. On the contrary there was a study completed on hamstring performance in female D3 athletes [4]. Six weeks long, this study found there to be no significant difference in power performance in either the stretching and control groups [4]. So maybe stretching just has an effect on sedentary individuals?

Another aspect of stretching that is renowned is its ability to decrease the body’s risk of injury. A study completed on patients with chronic neck pain had subjects undergo 6 weeks of stretching and/or global posture reeducation twice a week during that time [2]. After the study was completed it was found that both the stretching and posture reeducation groups had significant reduction in pain [2]. However, this study also lacked a control group so it is hard to tell whether the reduction in pain was at the result of a placebo effect. On the opposite end, a large scale literature search evaluated over 90 different studies trying to determine whether there was sufficient evidence that stretching does indeed reduce the risk of injury [3]. After reviewing a large amount of literature it was found that it cannot be determined whether stretching reduces the risk of injury [3]. In fact, it found it is more than likely to not have anything to do with injury risk because stretching depends on different characteristics of muscles than characteristics that rely on eccentric movement which is often the movement where non-contact injuries occur [3].

After reviewing the above literature and evaluating research that studied chronic stretching it really cannot be determined whether chronic stretching is essential in order to maintain performance and prevent injury. All of the studies observed either could not find data to support the fact that stretching indeed plays a pivotal role in exercise or the study was to limited in its structure to provide accurate results. The biggest problem was how the term, “chronic,” is defined. The longest study that we found was only 12 weeks long which can hardly represent professional athletes who have been stretching throughout their entire lives. Without longer studies it’s hard to determine anything about chronic stretching because there’s simply not enough data out there. Although stretching cannot be supported with factual scientific data it is hard to argue that it can’t hurt to stretch after exercise. With successful athletes swearing by its benefits why could it hurt to spend a little time after you exercise to stretch out? Even if it’s just for peace of mind stretching does have at least some benefit after all.

 

Questions to Consider:

In what populations is it most important to determine the effects of stretching?

Since most current studies are on the lower extremities, should studies been done on the effect of stretching the upper extremities ?

What would be your personal definition of chronic? Do you think 6 or 8 or 12 weeks studies count towards data for the effects of chronic stretching?

 

References and Further Readings:

  1. Kokkonen ’ J, Nelson AG, Eldredge C, et al. Chronic Static Stretching Improves Exercise Performance Chronic Static Stretching Improves Exercise. Performance Med Sci Sport Exerc. 2007;39(10):1825-1831. doi:10.1249/mss.0b013e3181238a2b.
  2. Aure OF, Hoel Nilsen J, Vasseljen O. Manual Therapy and Exercise Therapy in Patients With Chronic Low Back Pain. Spine (Phila Pa 1976). 2003;28(6):525-531. doi:10.1097/01.BRS.0000049921.04200.A6.
  3. Shrier I. Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science literature. Clin J Sport Med. 1999;9(4):221-227. https://www.colorado.edu/intphys/iphy3700/shrierCritRev.pdf. Accessed May 7, 2018.
  4. Bazett-Jones DM, Gibson MH, McBride JM. Sprint and Vertical Jump Performances Are Not Affected by Six Weeks of Static Hamstring Stretching. J Strength Cond Res. 2008;22(1):25-31. doi:10.1519/JSC.0b013e31815f99a4.
  5. Sainz de Baranda P, Ayala F. Chronic Flexibility Improvement After 12 Week of Stretching Program Utilizing the ACSM Recommendations: Hamstring Flexibility. Int J Sports Med. 2010;31(6):389-396. doi:10.1055/s-0030-1249082.
  6. Toland S. The Rise of Yoga in the NBA and Other Pro Sports | SI.com. Sports Illustrated. https://www.si.com/edge/2014/06/27/rise-yoga-nba-and-other-pro-sports. Published 2014. Accessed May 7, 2018.

Compression Clothing: Is it Worth It?

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In the last few years, compression clothing has become increasingly more popular, particularly among athletes. Used in conjunction with exercise and recovery, compression garments stabilize the soft tissue and are used in hopes of improved performance and reduced risk of discomfort or injury. To do so, they aim to alter intramuscular pressure through stress and strain to increase blood, and therefore oxygen, circulation. However, while some athletes find it helps during exercise or recovery, the actual benefits of compression clothing are debatable and require more research.

Current research focuses on the type of exercise performed while wearing the compression garments. For endurance athletes such as long distance runners, compression clothing had no significant changes in blood-oxygen concentration or blood lactate levels. However, for cyclists the compression clothing increased cycling performance along with StO2 output. The variance in success rates could be due to the motion of the athlete or the amount of time the clothing is worn. It also raises the question, how does the material impact the effectiveness of the garment?  The stress/strain forces between the garment and the skin creates a difference in pressure that only works when the compression is properly fitted. For the clothing to increase blood-oxygen levels there should be enough restriction to increase blood flow, but not so much that circulation could decrease. Finding the perfect material and fit for each athlete impacts effectiveness.

While there was no significant improvement in performance when wearing compression clothing during exercise, it may have a positive impact on an athlete’s recovery time. Many athletes saw benefits in wearing compression clothing after exercise to decrease muscle soreness. While this is not directly increasing oxygen intake, decreasing soreness can help athletes recover faster after exercise. Compression clothing is often used for medical purposes such as decreasing inflammation, which could explain why it works for sore muscles.

Based on current research, there is a lack of proof that compression clothing is beneficial during exercise.  The results can be impacted by the type of material used, fit, duration and type of exercise, or even the placebo effect, but there is still a lot to discover through measuring blood oxygen levels and recovery times in athletes wearing the garments.  Additionally, there does not seem to be a negative effect from wearing compression clothing.  If you are an athlete looking for a change in performance, compression clothing may not be your answer.  However, if you struggle with soreness or inflammation after exercise, you may benefit from wearing compression clothing.

Questions to Consider:

Have you used compression garments in conjunction with exercise? Recovery/injury?

If yes, did you find that they improved your experience compared to times when compression garments were not used?

Is there a potential health risk from using compression clothing?

Do the negatives of compression clothing (comfort, thermosensitivity, ergonomics) outweigh the positives? Is it worth wearing compression clothing for a slight change in performance?

How long does an athlete need to wear compression clothing to see a difference?

Further Reading:

Beliard S, Chauveau M, Moscatiello T, Cros F, Ecarnot F, Becker F. Compression Garments and Exercise: No Influence of Pressure Applied. Journal of Sports Science & Medicine. 2015;14(1):75-83.

MacRae B.A., Laing R.M., Partsch H. (2016) General Considerations for Compression Garments in Sports: Applied Pressures and Body Coverage. In: Engel F., Sperlich B. (eds) Compression Garments in Sports: Athletic Performance and Recovery. Springer, Cham

Engel F., Stockinger C., Woll A., Sperlich B. (2016) Effects of Compression Garments on Performance and Recovery in Endurance Athletes. In: Engel F., Sperlich B. (eds) Compression Garments in Sports: Athletic Performance and Recovery. Springer, Cham

Boucourt B, Bouhaddi M, Mourot L, Tordi N, Menetrier A. Changes in Tissue Oxygen Saturation with Calf Compression Sleeve: before, during, and after a cycling exercise. Journal of Sports Medicine. 2015 Dec;55(12):1497-501. Epub 2014 Oct 6.

Ali A, Caine M.P., Snow B.G. Graduated Compression Stockings: Physiological and Perceptual Responses During and After Exercise. Journal of Sports Sciences. 20 Feb 2007. 25(4): 413-19.

MacRae, Braid A., Cotter, James D., Laing, Raechel M. Compression Garments and Exercise. Sports Medicine. 07 Oct 2012. 41(10): 815-43.

Dermont T, Morizot L, Bouhaddi M, Ménétrier A. Changes in Tissue Oxygen Saturation in Response to Different Calf Compression Sleeves. Journal of Sports Medicine. 2015;2015:857904. doi:10.1155/2015/857904.

 

 

Effects of Protein Supplements on Muscle Recovery and Performance

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Many athletes and active individuals often seek the assistance of protein supplements post-exercise for a variety of reasons. Some take them in an effort to increase physical performance, while others aim to reduce muscle soreness and enhance the recovery process. However, the majority of these individuals decide to buy and consume these supplements based on marketing claims that are not backed by scientific research. This article outlines a literature study that examines the correlation between protein and the enhancement of muscular performance and recovery. The study takes into consideration healthy adults under the age of 50, and evaluates the effects of these supplements alone or in combination with carbohydrates on varying performance metrics.1 The results indicated that the continued use of protein supplements significantly reduced muscle damage and soreness after training sessions, and led to a particular increase in physical performance when participants were negative in nitrogen and energy balance.1 Other studies confirm the benefits of protein supplementation on muscle recovery and performance post-exercise, but at different degrees and with varying limitations.

This article relates to the course because it describes a study and application of the research process that addresses exercise-specific responses to physiological changes. Not only does it discuss and define the metabolic changes that arise from the use of protein supplements, but it also mentions the measurement of exercises and performance for comparison. It details a systematic approach to evaluating a problem through the collection of data, data processing, statistical analysis, evidence based results, and consideration of limitations.

Over the past few years, I have experimented myself with different protein supplements and exercise regimens to observe the potential effects on muscle growth and recovery. Although there are numerous factors that come into play, I agree with the claim that supplements are beneficial when used appropriately. However, diet, degree of activity, and frequency of use lead to large degrees of variation and pose a major limitation when comparing use among individuals. Regardless, much research should be carried out when deciding which protein supplement will be most successful for you and in achieving your goals.

Works Cited

[1] Pasiakos SM, Lieberman HR, McLellan TM. Effects of protein supplements on muscle damage, soreness and recovery of muscle function and physical performance: a systematic review. Sports Med. 2014 May;44(5):655-70. doi: 10.1007/s40279-013-0137-7. Review.

Nah Coach, I don’t have to stretch.

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Ever wondered if those pre- and post- workout sessions really make a difference in your daily exercise regimen? It is commonly believed that stretching prior to and following a workout will decrease the likelihood of injury, minimize post workout pain, and increase performance. However, other athletes and trainers believe that stretching has no impact on these factors and can even decrease strength and performance. But what are the facts?

Figure 1. Examples of active and passive/static and dynamic stretching.

There are several subgroups of stretching but I will focus on performance results with regards to the two most well researched types: static versus dynamic. Each stretch can be done actively or passively, where active stretching is when you contract the muscle in opposition to the one you want to stretch and passive uses an external force such as a strap, the force of your body weight, or gravity. Each type of stretching, shown above, has been shown to impact exercise in different ways. Let’s start with the most frequently used type, static stretching, where a person slowly moves muscles until they reach the brink of pain and hold that position for 20-30 seconds.

Static stretching has been compared to continuously stretching a rubber band. Immediately after stretching the rubber band, the band remains limp as it contracts slowly back into its original form, similarly to the behavior of a muscle. It seems unrealistic to expect a maximum amount of contraction and force immediately after stretching your muscle. In more physiological terms, the loss of muscular stiffness caused by static stretching results in an increase in length of sarcomeres in each muscle fiber, decreases contact between actin and myosin, and therefore decreases the force produced (Shrier, 2004; Kokhonen et al., 2004).

Figure 2. Actin and myosin movement in relaxed muscle versus contracted muscle. The less contact between actin and myosin, the less force produced.

One study by Fletcher and Jones (2004) on 97 male rugby union players showed a significant decrease in sprint times for the passive static stretch group. This could be due the mechanical impact of stretching on the muscle, kinematic differences, or neural inhibition which decreases the neural drive to muscle. Dynamic stretching focuses on moving through a range of motion repeatedly and mimics motion that will occur during exercise. Fletcher and Jones’ (2004) study showed more beneficial performance results from active dynamic stretching prior to sprinting though. The active dynamic stretch group of rugby players improved their sprint times significantly.

These results could be explained by information in a systematic review of studies on stretching and exercise by McGowan et al. (2015). This review showed that dynamic stretching increases the temperature of the muscle more than static stretching. This increase in temperature activated an increase in muscle metabolism, elevated oxygen uptake, and increased the power output of the muscle. Another study by Gray et al. (2008) showed a correlation between increased muscle temperature and faster ATP turnover, caused by an elevated rate of creatinine phosphate utilization and H+ accumulation. The elevated muscle temperature also resulted in short term (~2 minute) increase in anaerobic glycolysis and muscle glycogenolysis. These physiological responses, in theory, would result in greater power production during sprint and sustained high-intensity exercise, however high quality research results on this topic are limited.

Several literature reviews regarding this topic exist, but compiling results from hundreds of varying studies makes it difficult to normalize the results. Several reviews analyzed results that were not statistically significant, skewing the review results. By looking at the methods researchers used to gather and compile data and at the sources they cited, I was able to identify the sources where results were significant and relevant. The review also covered studies on a span of sports from swimming, to sprinting, to jumping, all which are impacted very differently by stretching, which makes the conclusions for these reviews far reaching statements. When more studies are done within each of these sports, reviews that group together specific events and exercises will provide more beneficial results.

When looking at the impact of stretching on pain, several papers used self-reported ratings of pain to measure differences. In those studies the results did not show a significant difference between ratings from groups that stretched and controls. Self-reported measurements of pain contain bias which makes them difficult to compare between groups of people. Some papers overcame bias by observing differences in delayed muscle soreness by measuring creatine kinase levels, a commonly used marker for muscle damage. One experiment by Buroker and Schwane (1989) showed no significant difference in creatine kinase levels from stretching post-exercise. Very few studies are done solely to measure the effect of post-exercise stretching on soreness and risk of injury so it is difficult to differentiate these results from the pre-exercise stretching.

Keeping these biases and knowledge gaps in mind when considering the results of these papers, it is plausible that for the majority of exercises, dynamic stretching can positively impact your performance. This is largely due to the fact that it increases the core body temperature and targets activity in specific muscles that will be used instead of just stretching them. Static stretches prior to a workout seem to have no impact or a negative impact on performance since the muscle needs time to recover and regain stiffness before use. Personally, this would convince me to do some dynamic stretches before my next run rather than static stretches. While it differs from sport to sport, dynamic stretching appears to be the ideal pre-exercise stretch to optimize performance.

Recommended Further Reading:

1. Blahnik, Jay. Full-Body Flexibility, Second Edition. Available at: http://www.humankinetics.com/excerpts/excerpts/types-of-stretches

2. Sifferlin, Alexandra. Why Stretching May Not Help Before Exercise. (April 08, 2013) Available from: http://healthland.time.com/2013/04/08/why-stretching-may-not-help-before-exercise/

3. Shrier, Ian. Sports Med (2004) 14:267-273. Available from: http://www.elitetrack.com/article_files/stretchingreview.pdf

4. Kokkonen,  J.,  Nelson,  Α.  G.,  Cornwell,  Α.  (1998). Research Quarterly for Exercise and Sport. 69 (4): 411-415. Available from: https://www.ncbi.nlm.nih.gov/pubmed/9864760

5. Fletcher, IM, Jones, B. J Strength and Condition Research. (2004) 18(4), 885-888. Available at: http://staps.nantes.free.fr/L3/entrainement/etirements/THE%20EFFECT%20OF%20DIFFERENT%20WARM-UP%20STRETCH.pdf

6. McGowan, C.J., Pyne, D.B., Thompson, K.G. et al. Sports Med (2015) 45: 1523. Available at: https://link-springer-com.udel.idm.oclc.org/article/10.1007%2Fs40279-015-0376-x

7. Gray, SR, Soderlund, K, Ferguson, RA. J Sports Sci. (2008) 26(7):701:7. Available at: https://www-ncbi-nlm-nih-gov.udel.idm.oclc.org/pubmed/18409101?dopt=Abstract

8. Buroker, KC, Schwane, JA. The Physician and Sportsmedicine (1989) 17(6): 65-83. Available from: http://www.tandfonline.com/doi/citedby/10.1080/00913847.1989.11709806?scroll=top&needAccess=true