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Thank you for being part of our community. ASEP is the specific voice for (historically under-represented) Exercise Physiologists.
Please use this Newsletter as a link to ASEP resources from scientific
journals to professional papers, to employment and related
opportunities. And be sure to click on "More On Us" at the left for the
ASEP-newsletter's parent web site.
-Lonnie Lowery and Jonathan Mike, ASEP-Newsletter Editors |
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Editor's Corner |
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 Exercise Physiology and Nutrition: Bringing Down the Wall
November
9, 2009 saw the 20th anniversary of the fall of the Berlin Wall, which
created an improved flow of ideas between East and West. During those
same 20 years, there have been the beginnings of a similar movement in
academics. Universities have begun restructuring departments and
removing barriers around a perhaps inevitable purpose: improved
cross-talk among professionals in allied health.
To
the academic Exercise Physiologist, student or instructor, this could
mean a change in thinking from a classical physical education model
(housed within a College of Education) to a structure that is arguably
more problem oriented. And EPs have plenty to offer regarding the
health problems of society. Whether it's obesity, cardiovascular
disease, diabetes, cancer, depression, or a host of other conditions,
there is a natural synergy between exercise physiology and nutrition.
One
need only briefly look at the U.S. "My Pyramid" (Food Guide) or the
Dietary Guidelines for Americans to notice specific exercise physiology
symbolism and recommendations. Why is exercise physiology presented to
the public as "food" or "dietary" guidelines? Perhaps because of the
"silos" that EPs have worked in for so long. Licensed health
professions like Dietetics have taken the public lead while EPs have
spent time in relatively isolated labs generating data used to promote
such professions and their public health messages.
Creating
the evidence for "evidence-based practice" is noble but it's
increasingly dawning on university administrators that exercise
physiologists cannot be separated from their nutrition colleagues when
it comes to optimally and directly addressing some of society's biggest
killers. In fact, combined exercise-nutrition interventions are not
just better but often far better than either modality alone. It's a
powerful combination. I'm fond of telling my own dietetics students
that "exercise changes the body from the sub-cellular level, on up".
And yet, alas, they currently get but a single course on sports
nutrition - mostly focused on athletic performance.
For
this reason and others, my University has joined nearby institutions in
beginning serious discussions on combining and restructuring
health-related departments, including Exercise Science and Wellness
(with its physical education roots) and Nutrition-Dietetics (with its
home economics roots). I imagine that, if one looks across the U.S. and
other nations, these department types have evolved over time and now
often overlap in research endeavors and course material.
With this in mind, it's strange that the wall has not come down sooner.
Lonnie M. Lowery, PhD, RD
ASEP-Newsletter Editor
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| Ask the EP |
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Q: Can
you explain the physiology of Lactate Threshold and Ventilation
Threshold? Are there other influential factors involved with these
measures and training protocols?
Lactate
threshold (also termed anaerobic threshold) is the exercise intensity
that is associated with a substantial increase in blood lactate during
incremental exercise testing. (1). Maximal lactate steady state refers
to the exercise intensity that corresponds to the highest blood lactate
concentration that exists before a continual increase occurs. These
terms are also used interchangeably with the onset of blood lactate
accumulation or 'OBLA' (2,3). Muscle metabolism changes considerably
during incremental exercise as does lactate concentration and
alterations in blood pH. Blood samples are used during these protocols
to measure and locate the exercise intensity after which lactate begins
to accumulate. The exercise intensity at the lactate threshold has been
interpreted as representing the maximal steady state exercise intensity
and has been shown in the literature to be the best predictor of
prolonged exercise (4).
Other approaches (non-invasive measures) of
the lactate threshold using indirect calorimetry and expired gas
analysis are also be performed. In short, as acidosis occurs the volume
of carbon dioxide (VC02) increases due to buffering of bicarbonate ions
((HCO3). In turn, the abrupt decline in blood pH and the rise in VC02
accelerate ventilation that is disproportionate to the linear increase
in V02 (5,6,7).
Historically, increases in lactate have been
considered an indication of increased anaerobic metabolism due to low
O2 levels in the muscle cells (8). However, there are several proposed
explanations for the lactate threshold. There include but are not
limited too:
- Decreased removal of lactate from circulation
- Increased reliance on type 2 muscle fibers
- Difference between the rate of glycolysis and mitochondrial respiration.
- A decrease in redox potential; increases in NADH relative to NAD+
- Muscle hypoxia (low muscle 02 content)(9)
The exercise intensity at which there
is a simultaneous deviation from linear progression in ventilation and
an increase in VE/V02 is described as Ventilatory Threshold (VT),
(5,6,7). Caizzeo (5) have demonstrated that the joint VE and VE/V02
criteria are most sensitive in detecting VT. The traditional
explanation of the VT is that as exercise intensity increases, an
increase in metabolic acidosis occurs after the lactate threshold
causes an increase in blood acidosis and PA C02. Both the acidosis and
PA C02 stimulate chemoreceptors, thereby increasing ventilation,
although the exact mechanisms are still unknown.
Interestingly,
Ventilation and LT can be detected when graphing the VE/V02 to V02
(x-axis) or by graphing the VC02 to V02 (x axis), which is called the
V-slope method. (5)
Numerous studies have demonstrated the
comparison of LT and VT (10,11,12,8) and concluded the two measures are
identical (5,8,13,14). Other research concluded the opposite, and
stress the two criteria should not be used as a trade off
(15,11,16,12). However, factors considered that can cause differences
in VT and LT, include but are not limited too: altered carbohydrate
intake, variation in exercise protocols, enzyme deficiency, increase
altitude, and exercise training. It is estimated VT and LT may differ
8% of VO2 max, which is important when prescribing exercise intensity
(17).
Methods that plot changes in ventilation, or are
influenced by ventilation, can be influenced by individual differences
in the multiple determinants of ventilation during incremental
exercise. However, the V-slope method has not been validated by
comparison to blood lactate thresholds. Evidence indicates that all
methods of VT detection are influenced by the exercise protocol,
methods of detection and evaluator (18).
Both VT and LT can be
used to guide training intensity or pace. They can also be more
responsive indicators of training improvement than V02 max. Generally,
trained endurance athletes have higher VT's on a treadmill compared
with cycle ergometry, whereas the VT in trained cyclists does not
differ between running and cycling. Speculation exits in differences
between LT during running and cycling for triathletes or biathletes
because they are trained in both modes. Although research is minimal
Albreight and colleagues (19) showed no differences between LT in
running and cycling in triathletes.
Jonathan Mike, MS, CSCS, USAW, NSCA-CPT,
Doctoral Student, Assistant Editor
References
1). Svedahl K, MacIntosh
BR. Anaerobic threshold: the concept and methods of measurement. Can J
Appl Physiol. 2003 Apr;28(2):299-323. Review
2). Heck H, Mader
A, Hess G, Mucke S, Muller R, Hollmann W. Justification of the 4-mmol/l
lactate threshold. Int J Sports Med. 1985 Jun;6(3):117-30
3). Mader A, Heck H. A theory of the metabolic origin of "anaerobic threshold".
Int J Sports Med. 1986 Jun;7 Suppl 1:45-65
4).
Robergs, R.A., Keteyian,S.J. (2003). Fundamentals of Exercise
Physiology: For Fitness Performance and Health. New York: The
Mcgraw-Hill Companies.
5). Caiozzeo VJ, Davis JA, Ellis JF, Azus JL, Vandagriff R, Prietto CA, McMaster WC.
A comparison of gas exchange indices used to detect the anaerobic threshold.
J Appl Physiol. 1982 Nov;53(5):1184-9
6).
Beaver WL, Wasserman K, Whipp BJ. A new method for detecting anaerobic
threshold by gas exchange. J Appl Physiol. 1986 Jun;60(6):2020-7
7).
Caputo F, Mello MT, Denadai BS. Oxygen uptake kinetics and time to
exhaustion in cycling and running: a comparison between trained and
untrained subjects.
Arch Physiol Biochem. 2003 Dec;111(5):461-6.
8). Wasserman, K, Mcilroy, MB. Detecting the threshold of anaerobic metabolism .Am J Cardiol. 1964 Dec;14:844-52.
9).
Powers, SK. Howley,ET. (2004, 5th ed). Exercise Physiology: Theory and
Application to Fitness and Performance. New York: The Mcgraw Hill
Companies
10). Dempsey JA. . Is the lung built for exercise? Med Sci Sports Exerc. 1986 Apr;18(2):143-55. Review
11).
Farrell SW, Ivy JL. Lactate acidosis and the increase in VE/VO2 during
incremental exercise. J Appl Physiol. 1987 Apr;62(4):1551-5.
12).
Neary PJ, MacDougall JD, Bachus R, Wenger HA. The relationship between
lactate and ventilatory thresholds: coincidental or cause and effect?
Eur J Appl Physiol Occup Physiol. 1985;54(1):104-8
13).
Wasserman K, Whipp BJ, Koyl SN, Beaver WL. Anaerobic threshold and
respiratory gas exchange during exercise.J Appl Physiol. 1973
Aug;35(2):236-43
14). West J.B. Respiratory Physiology: The Essentials. 5th ed. Lippincott Williams and Wilkins, Philadelphia, 2004
15).
Anderson GS, Rhodes EC. Relationship between blood lactate and excess
CO2 in elite cyclists. J Sports Sci. 1991 Summer;9(2):173-81
16).
Gaesser GA, Poole DC. Lactate and ventilatory thresholds: disparity in
time course of adaptations to training. J Appl Physiol. 1986
Sep;61(3):999-1004
17). Gladden LB. Lactate metabolism: a new paradigm for the third millennium.
J Physiol. 2004 Jul 1;558(Pt 1):5-30. Epub 2004 May 6. Review.
18).
Whipp BJ, Ward SA. Physiological determinants of pulmonary gas exchange
kinetics during exercise. Med Sci Sports Exerc. 1990 Feb;22(1):62-71.
Review
19). Albrecht, T.J; V.L. Foster, A.L. Dickinson, and
J.M. DeBever. Triathletes: Exercise Parameters during bicycle, swim
bench, and treadmill testing. Medicine and Science in Sports and
Exercise. 18(2): S86, 1986
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Opportunities Related to Exercise Physiology
The Department of Kinesiology at the University of New Hampshire...
is currently seeking applicants for a tenure track appointment in
Exercise Science at the Assistant or Associate Professor level. ...more information...
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Thank you for perusing our opinions, facts and opportunities in this edition of the ASEP-Newsletter.
Sincerely,
Lonnie Lowery
American Society of Exercise Physiologists |
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