Low Bone Mass in ROAD Cyclists and Ways to Fix it

It may come to a surprise that many professional road cyclists are at risk for osteoporosis.  Even with their amazing endurance and the ability to maintain very high power, being in a non weight-bearing position for extended periods of time is not conducive towards maintaining healthy bone mass density (BMD) (2).  In a study by Bryant et al, 30 professional road cyclist (~29 years old) were compared to 30 young healthy males of similar age.  When comparing BMD values from multiple sites, they found that professional road cyclists had a similar head BMD, but saw lower values in the following locations:

• Arms
• Legs
• Spine
• Pelvis
• Lumbar Spine
• Femoral neck (most affected site -18%)

Road cyclists who neglect strength training are at risk for osteoporosis and may already be osteopenic:
Another study produced similar results.  Smathers et al. measured total body, lumbar spine and proximal femur BMD in male competitive road cyclist and compared their values to age-/ body mass-matched controls.  Despite having at least 9.4 years of racing experience and 7-22 hours per week of training, the cyclist's t-scores indicated that 9% of the cycling group and 3% of the control group were classified as osteoporotic (5).  In terms of osteopenia, 25% and 10% of the cycling and control group, respectively, were osteopenic (5).

Greater Problem with Master Road Cyclists
Differences in BMD was even more prominent when master cyclists were compared to age matched controls.  In a study performed by Nichols et al, master cyclists with a minimum of 10 years of training who performed little weight-bearing exercise were measured at the spine and total hip.  Both sites were significantly lower compared to the age matched controls.  This study showed that although the master cyclist were highly trained and physically fit, they were still at risk for developing osteoporosis with advancing age (4).

Mountain Cyclists vs. Road Cyclists
I want to emphasize that decreased bone mass density was found only in road cyclist who performed little to no weight bearing exercises.  Mountain cyclist may not have to worry about low bone mass density.  In a study specific to mountain cyclists, BMD values at the proximal femur, lumbar spine and the total body were higher than the controls (7).  The sharp forces experienced through mountain biking may provide the stimulus necessary to cause bone to adapt.

Runners vs Cyclists

Running was associated with increased bone density, especially in the leg (6).  Again, cycling was associated with a mild decrease in BMD of the total body and lumbar disks L1-L4 (6).  The results show that high impact activities such as running, plyometrics and power exercises may generate loads several times the body weight- enough strain to stimulate adaptation of the bone (2,6).

Ways to Improve BMD
Many road cyclists have a "ride more" attitude, and will avoid strength training, fearful that the fatigue will cause them to lose riding time.  In reality, a cycling program that includes heavy weight lifting actually improves endurance in elite athletes (8).  As I described in a separate post about lifting weights to improve endurance, heavy weight lifting recruits both slow and fast twitch muscle fibers.  This is why strength training alone can produce significant improvements in VO2max and muscular endurance.

Implement these points to your cycling program for a healthy BMD:

• Include heavy weight lifting (at least 8 RM) or any load that is greater than what's encountered on a daily basis (2).
• Perform strength exercises in a standing posture such as squats, lunges, long jumps, box jumps, etc.
• Use free weights or a weighted vest at 7-15% body weight (2).
• Emphasize exercises that improve muscular strength and power (2)
• Participate in high-impact, group exercise classes (aerobic, boot camp, zumba, etc.)
• Plyometrics.  Studies have shown that simple jumping exercises may increase bone mass, especially at the hip (9,10,11,12).

If spine BMD or bone status are unknown, see these exceptions to the suggestions above:

• Avoid heavy loads (>10% body weight) (2).
• Avoid high impact plyometrics (>2.5 times body weight)
• Avoid loads greater than 8RM

References:

1. Applied anatomy and biomechanics in sport. New York: Blackwell Scientific Publications, 1994. Print.
2. Bryant, Cedric X., and Daniel J. Green. ACE advanced health & fitness specialist manual: the ultimate resource for advanced fitness professionals. San Diego: American Council On Exercise, 2008. Print.
3. Campion, F., A.M. Nevill, M.K. Karisson, J. Lounana, M. Shabani, P. Fardellone, and J. Medelli. "Bone Status in Professional Cyclists."International Journal of Sports Medicine Sep. 2010: 511-515. Print.
4. Nichols, Jeanne, Jacob Palmer, and Susan Levy. "Low bone mineral density in highly trained male master cyclists."International Osteoporosis Foundation and National Osteoporosis Foundation July 2003: 644-649. Print.
5. Smathers, Aaron, Michael Bemben, and Debra Bemben. "Bone Density Comparisons in Male Competitive Road Cyclists and Untrained Controls."Medicine & Science in Sport & Exercise Feb. 2009: 290-296. Print.
6. Stewart, Arthur, and James Hannan. "Total and regional bone density in male runners, cyclists, and controls."Medicine & Science in Sports & Exercise Aug. 2000: 1373-1377. Print.
7. Warner, S.E., J.M. Shaw, and G.P. Dalsky. "Bone mineral density of competitive male mountain and road cyclists."Bone Jan. 2002: 281-286. Print.
8. Hickson R., Dvorak B., Gorostiaga E., Kurowski T. & Foster C. (1988) Potential for strength and endurance training to amplify endurance performance. Journal of Applied Physiology 65, 2285-2290.
9. Bassey, E.J. & Ramsdale, S.J. (1994). Increase in femoral bone density in yound women following high impact exercise. Osteoporos International, 4, 2, 72-75.
10. Bassey, E.J. et al. (1998). Pre- and postmenopausal women have different bone mineral density responses in the same high-impact exercise. Journal of Bone Mineral Research 13, 12, 1805-1813.
11. Heikkinen, R. et al. (2007). Acceleration slope of exercise-induced impacts is a determineant of changes in bone density. Journal of Biomechics. 40, 13, 2967-2974.
12. Winters, K.M. & Snow, C.M. (2000). Body composition predicts bone mineral density and balance in premenopausal women. Journal of Women's Health and Gender-Based Medicine, 9, 8, 865-872.

Weight Training Methods for Muscular Endurance

While lifting for 12-15 reps at approximately 60% 1RM is great for developing localized strength and endurance within specific muscle groups, there are other methods just as effective at improving muscular endurance.  If you lift regularly with minimal to no professional supervision, I recommend avoiding method #1, heavy weight training.  Same recommendation follows for variable load training unless you decrease the load. 

1. Heavy weight training
• 80-90% 1RM, 4-8 repetitions.
• 100% 1RM produces the greatest improvements in both endurance and strength, but greatly increases risk of injury.
2. High repetition training
• 30-50% 1RM, 30-50 repetitions, 3-4 sets
• May be used to develop power.  Reps and sets may stay the same, but use a load of 30% 1RM for optimal power development.  Full rest between sets is required.
• A variation of this set to a time limit (interval training)
3. Variable load training
• Combines both methods.  Progressively lower loads are lifted consecutively with little to no rest.  Repetitions depends on the load.
• First load focuses on strength- 66% 1RM or higher
• Last load focuses on lactic acid production- 30-50% 1RM

1. HEAVY WEIGHT TRAINING:  Contrary to popular belief, lifting heavy weights for a few repetitions will not just improve muscular strength, it will also improve endurance.  Lifting heavy weights will improve endurance because all motor units must be recruited to complete the lift, that means both fast and slow twitch muscle fibers will be activated (2,7).  For this reason, it is widely accepted that there is a strong relationship between muscular strength and endurance (1,2).

I was skeptical about this method at first, but it made sense after I realized that the physiological changes that occur with heavy weight lifting are similar to that of endurance training.  The structural changes that occur with heavy weight training include increased number/ size of myofibrils, number of actin/ myosin and the size/ strength of tendons, ligaments and connective tissue (2,4).  In addition to these anatomical changes, anaerobic metabolism also improves through increased levels of creatine phosphate, glycogen and creatine phosphokinase (4).  All of these changes allow the muscle to operate with less effort to do the same amount of work.

To make it easier to understand how effort is reduced, I calculated two realistic changes in 1RM that could occur with heavy weight lifting.  Let's say that a cyclist needs to produce 50 pounds of pedal force to maintain a hard pace.  If the cyclist had a 1RM of 200 pounds, then it would take 25% of maximal effort to maintain that hard pace.  After spending time with heavy weight lifting, the cyclist improved the 1RM to 230 pounds.  Next time the cyclist tries to maintain that hard pace, it will feel easier because instead of using 25% of maximum, only 21.7 % is needed to maintain that pace.

• Initial maximal strength:  1RM = 200 lbs / 1 repetition
• Cycling requirement:  50 lbs / pedal stroke = 25.0% of maximum
• Improved maximal strength:  1RM = 230 lbs / 1 repetition
• Cycling requirement:  50 lbs / pedal stroke = 21.7% of maximum

Being able to operate at a lower percentage of maximum is a clear advantage that endurance athletes can take advantage of.  To reap the benefits of this method, a weight greater than 66% of 1RM must be used (3).  For the greatest possible improvement in strength, use 100% 1RM (2).  If you choose to lift 100 percent, please be smart and get a spotter!

2.  HIGH REPETITION TRAINING:  High repetition training or HRT involves three to four sets of lifting relatively light weights (30-50% 1RM) anywhere from 30 to 50 times.  This is a popular method for increasing muscular endurance because the training effects are more obvious and easier to understand.  High repetition training improves muscular endurance through four mechanisms different from the method above:

1. HRT produces more lactate than the levels found in competition
2. Improves the individual's tolerance to the fatiguing effects of lactate
3. Promotes local circulation to the working muscle group(s)
4. Enhances metabolism and other by products

Of the three mechanisms, one and two are the major reasons why it's important to implement this type of training to a program.  Greater tolerance to lactate is advantageous to anyone who needs to work at high intensities for a long time.  This will translate to better performance in competition and training.  I also wanted to mention that the load recommended for this type of training is very similar to the optimal load for maximal power training (approximately 30-45% 1RM) (2).  For the greatest improvement in power, studies have found that 30% of maximum will optimally improve power (5,6).  To specifically improve power-endurance, the repetitions may also be performed explosively.

Another variation of this method involves completing the greatest number of repetitions within a set time.  For example, a 5k runner will likely run 400 meters in 50 seconds repeatedly.  This variation might sound familiar because it is essentially "interval training."

3.  VARIABLE LOAD TRAINING:  This method combines the best of both worlds that heavy weight training and high repetition training can offer.  Because methods one and two produce similar improvements in muscular endurance, this type of training is an excellent way to reap both of the benefits (2).  To perform this type of training, a number of progressively lighter loads should be performed consecutively with little to no rest.  The first load(s) must be higher than 66% 1RM to improve maximal strength gains (3).  The final load(s) should be 30-50% 1RM to increase lactic acid production and improve tolerance to the effects of lactic acid.  Successfully lifting all of the loads marks the end of the first set.  See the sample program below.

• 10 repetitions/ 80% 1RM
• 12 repetitions/ 60% 1RM
• 15 repetitions/ 40% 1RM
• 10 repetitions/ 30% 1RM explosive

References:

1. Anderson T. & Kearney J. (1982) Effects of three resistance training programmes on muscular strength and absolute and relative endurance.  Research Quarterly for Exercise and Sport 53, 1-7.
2. Applied anatomy and biomechanics in sport. New York: Blackwell Scientific Publications, 1994. Print.
3. McDonagh M. & Davies C. (1984) Adaptive response of mammalian skeletal muscle to exercise with high loads. European Journal of Applied Physiology 52, 139-155.
4. Plowman, Sharon A., and Denise L. Smith. Exercise physiology for health, fitness, and performance. 3rd ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2011. Print.
5. Kaneko M., Fuchimoto T., Toji H. & Suei K. (1983) Training effect of differing loads on the force-velocity relationship and mechanical power output in human muscle. Scandinavia Journal of Sport Science 5, 50-55
6. Moritani T., Muro M., Ishida K. & Taguchi S. (1987) Electrophysiological analyses of the effects of muscle power training. Research Journal of Physical Education in Japan 1, 23-32.
7. Schmidtbleicher D. & Haralambie G. (1981) Changees in contractile properties of muscle after strength training in man. European Journal of Applied Physiology 46, 221-229.

How to Calculate Target Heart Rate Zones

Keep things simple with three zones.

• If you want a quick and convenient method, use the NASM three zone system.  Assign a zone for each metabolic system: the ATP-PC, lactic acid and aerobic system.

Determine the lactic threshold zone first, then aerobic and ATP-PC zones.

• Lactic threshold can occur anywhere from 75 percent to 85 percent of HRmax (1).  After finding the heart rate that represents lactic threshold, keep the LT zone within a 5% upper and lower limit.
• My LT Test: If your scared of needles like me, try the test I created to estimate lactic threshold.  Be sure you're cleared by a physician before performing any maximal-effort test.  After a five minute warm up, ride at a maximal, steady effort for 12 minutes.  Why 12 minutes?  The test needs to be short enough to prevent cardiac drift and local muscle fatigue.  Record heart rate at three minute intervals.  The average of the last three measurements will give you a good estimate of lactic threshold.  Add and subtract 5% to create the upper and lower limit of the LT zone.  End the test with a 5-10 minute progressive cool down.

Don't give more than 100 percent.

• The American College of Sports Medicine found that intensities above 100% HRmax produced smaller improvements in VO2max than intensities that are within 90-100% HRmax (4).  It's also important to consider that intensities above 100% HRmax will also increase the risk of overtraining.

Recovery should feel like recovery.

• Don't assign a minimum value to the recovery zone.  If 65% HRmax feels too hard, it's ok to go lower, especially if it limits your ability to complete all intervals, or adds fatigue.

If you're exercising just for the health benefits:

• The ACSM heart rate zones are more appropriate for people new to exercise- not athletes.  The conversions from HRmax to HRR/ VO2R to RPE are very convenient.

Below are the THR zone recommendations from different sources.

Long-Distance Cycling by Dr. Burke & Ed Pavelka.  I was very happy with this book when they mentioned that the border (LT) between zones two and three differs based on individual differences.  An untrained cyclist may hit lactic threshold at 75% and an elite cyclist might reach LT at 85%.  Dr. Burke and Mr. Pavelka gave excellent advice regarding individual differences with LT and I liked that they recommended zones specific to each metabolic system.

• Zone 1: Recovery = <65% HRmax
• Zone 2: Aerobic endurance = 65% - 84% HRmax 
• Zone 3: Lactic threshold = 85% - 94% HRmax
• Zone 4: Anaerobic = 95% - 100% HRmax

Mastering Cycling by John Howard.  Based on the way the zones were described, it seemed like the heart rate recommendations were based more on opinion than research findings.  I would have liked this section more if the book mentioned that individual differences can throw off all of the ranges and provided suggestions to modify each zone.

Although the heart rate recommendations were a little iffy, I liked that he provided FTP "functional threshold power" recommendations based on Dr. Andrew Coggan and Hunter Allens book called Training and Racing with a Power Meter.  If you're unfamiliar with FTP, it's the maximum amount of power that can be held for an hour.  Unlike lactic threshold and ventilatory threshold, functional threshold power is a measurement of a mechanical variable, not a physiological one.  The functional threshold is the point where heart rate increases and power decreases; in other words, the point where you are fatigued.  Anyway, here are the recommendations below.

• Zone 1: Active Recovery = 50 - 60% HRmax, ~55% FTP
• Zone 2: Endurance = 70% HRmax, 56-75% FTP
• Zone 3: Tempo = 60 - 70% HRmax, 76-90% FTP
• Zone 4: Sweet Spot = 75 - 80% HRmax, no FTP recommendations...
• Zone 5: VO2 max = 80 - 85% HRmax, 106-120% FTP
• Zone 6: Anaerobic Capacity = 85 - 95% HRmax, 121-150% FTP
• Zone 7: Neuromuscular Power = >95% HRmax, >150% FTP

American College of Sports Medicine, 1998.  Based on 20-60 min for 3-5 days per week.  Interval training programs with intensities 90-100% of VO2max lead to the greatest amount of improvement in VO2max.  Exceeding 100% will produce smaller improvements than the 90 to 100 percent range.

• Very light: <35% HRmax
• <20% HRR/ VO2R (<10 RPE)
• Light: 35-54% HRmax
• 20-39% HRR/ VO2R (10-11 RPE)
• Moderate: 55-69% HRmax
• 40-59% HRR/ VO2R (12-13 RPE)
• Hard: 70-89% HRmax
• 60-84% HRR/ VO2R (14-16 RPE)
• Very Hard: greater than or equal to 90% HRmax
• Greater than or equal to 85% HRR/ VO2R (17-19 RPE)
• Maximal: 100% HRmax
• 100% HRR/ VO2R (20 RPE)

National Academy of Sports Medicine 2010. These ranges were determined through respiratory quotients (RQ).  Respiratory quotient is calculated by dividing the volume of CO2 produced by the volume of O2 consumed.  This is a good way to measure effort and the dominant energy system.

• Zone 1: Recovery/ Low Intensity = 65-75% HRmax or RQ 0.80-0.90
• Zone 2: Anaerobic Threshold (AT)/ Higher Intensity = 80-85% HRmax or RQ 0.90-1.0
• Zone 3: Above AT / High Intensity = 86-90% HRmax or RQ > 1.0

Resources:

1. Burke, Ed, and Ed. Pavelka.The complete book of long-distance cycling: build the strength, skills, and confidence to ride as far as you want. Emmaus, Pa.: Rodale ;, 2000. Print.
2. Clark, Micheal, Scott Lucett, and Donald T. Kirkendall.NASM's essentials of sports performance training. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins, 2010. Print.
3. Howard, John. Mastering cycling. Champaign, IL: Human Kinetics, 2010. Print.
4. Thompson, Walter R., Neil F. Gordon, and Linda S. Pescatello. ACSM's guidelines for exercise testing and prescription. 8th ed. 

How To: Heart Rate Training

Determining Max Heart Rate

The most well known equation that estimates maximum heart rate is:

220 - age = HRmax

This equation assumes that everyone loses one beat per minute from their maximum heart rate for every year they get older.  Since this rate of loss does not apply to everyone, this equation has a large standard deviation (+/- 12-15 bpm).  For people younger than 40 years old, this equation underestimates HRmax; for people older than 40 years old, this equation overestimates HRmax (5).

The most accurate HRmax equation (2) is not as easy to remember, but it will give a better estimate than the equation above:

206.9 - (0.67 x age) = HRmax

Target Heart Rate Equations:

The first equation involves simple multiplication:

THR = HRmax * desired percentage

The method below factors resting heart rate into the equation.  For this reason, the equation below is more accurate ONLY if the resting heart rate is measured accurately.  As mentioned in the post about the limitations of heart rate training, several variables may cause heart rate to vary as much as 1 - 6 bpm from day to day (1,3,4).  For this reason, the equation below requires daily updating to account for this variability.  Otherwise, training intensity might be too high or low; potentially targeting the wrong metabolic system, and producing the wrong training effect.

THR = ((HRmax - HRrest) x desired percentage) + HRrest

I recommend using this equation anytime you notice a detectable change in resting heart rate.

Resources:

1. Astrand, P.-O. and Saltin, B. (1961). Oxygen uptake during the first minutes of heavy muscular exercise. Journal of Applied Physiology, 16, 971-976.
2. Gellish, RL, Goslin B.R., Olson R.E., McDonald A., Russi G.D., Moudgil V.K. Med Sci Sport Exercise. 2007;39(5):822-9.
3. Lambert, M.I., Z.H. Mbambo, and A. St Clair Gibson. "Heart rate during training and competition for long-distance running." Journal of Sports Sciences 16 (1998): S85-S90. Print.
4. Selley, E.A., Kolbe, T., Van Zyl, C.G., Noakes, T.D. and Lambert, M.I. (1995). Running intensity as determined by heart rate is the same in fast and slow runners in both the 10- and 21-k, races. Journal of Sports Sciences, 13, 405-410.
5. Thompson, Walter R., Neil F. Gordon, and Linda S. Pescatello. ACSM's guidelines for exercise testing and prescription. 8th ed. Philadelphia: Lippincott Williams & Wilkins, 2010. Print.

Heart Rate Training Limitations and Phenomena

With the advances in technology, heart rate monitors have the ability to measure heart rate with ECG (electrocardiogram) accuracy.  To get the most out of heart rate training, its important to be aware of various phenomena and limitations leading to misinterpreted data.

1. 220 - age = HRmax?  Recommended by the American College of Sports Medicine (ACSM) to estimate maximal heart rate, it has a large standard deviation of plus or minus 12-15 bpm (4,5).  I highly recommend using RPE in conjunction with this method to determine if your HR max was under- or overestimated.
2. Cardiac drift & Training in heat.  Cardiac drift is a phenomena that causes changes in HR and SV (strove volume) to occur when exercise exceeds 30 minutes at the same workload.  With the onset of heat stress, SV drops due to vasodilation, plasma loss, and circulatory changes.  Collectively, this occurs to improve heat removal.  To compensate for lower SV, HR increases to maintain cardiac output (2,3,4).  In a study on competitive cyclists, cardiac drift caused HR to increase by 20 bpm from 20-60 minutes of exercise (2).  The takeaway is that after 30 minutes of constant aerobic exercise at the same intensity, heart rate will increase without a change in effort or RPE.  This also means that temperature and humidity can also affect heart rate significantly since it directly affects thermoregulation.
3. Dehydration increases heart rate.  During moderate dehydration, it was estimated that for every 1 percent loss of body weight caused by dehydration, heart rate increased 7 beats per minute (1).  A study which required subjects to exercise at 62-67% VO2max for over 100 minutes with no fluid intake found that heart rate increased by 40 bpm (10).  When the subjects were allowed to hydrate, heart rate only increased by 13 bpm (10, 11).  If the difference between hydration and dehydration wasn't clear before, it should be clear now!
4. Heart rate varies daily.  Under the same workload, heart rate can vary anywhere from 1-6 beats per minute (1,3,6).  This variation may be affected by a combination of things such as the environment, motivation, time of the day, hydration levels, nutrition, sleep and medications (3).  This is another good reason to use RPE to keep workouts honest.
5. At the same workload, heart rate in competition is higher than in training (6).  Studies have found that during competition, there is no relationship between heart rate and running speed (3,4,5).  In a 10 km distance, heart rate was 163 bpm (+/- 13 bpm) in competition and 143 bpm (+/- 22 bpm) in training (9). Because heart rate values in training are typically lower, runners tend to unerestimate their pace on race day.  A study targeted towards cycling found that cyclists consistently reached higher maximal heart rates in competition compared to the laboratory determined maximum heart rates (4).  Motivation and pacing could explain this variation.  Paying attention to your pre-race nerves can help with deciding whether your heart rate zones need to be shifted higher or lower.
6. Medications can increase or decrease heart rate.  Stimulants such as caffeine, amphetamines, ephedrine, psudoephedrine and cocaine can also increase heart rate (8).  Beta blockers or Beta-adrenergic blocking agents can lower heart rate (7).

Despite the limitations of heart rate training, heart rate monitors have the potential to provide extremely useful information that can improve the quality of training, track progress and most importantly, prevent overtraining.  As you learn how nutrition, hydration, psychology affects heart rate, the data will become much more reliable for training and racing.

Resources:

1. Astrand, P.-O. and Saltin, B. (1961). Oxygen uptake during the first minutes of heavy muscular exercise. Journal of Applied Physiology, 16, 971-976.
2. Jeukendrup, Asker, and Adrie Van Diemen. "Heart rate monitoring during training and competition in cyclist." Journal of Sports Sciences 16 (1998): S91-S99. Print.
3. Lambert, M.I., Z.H. Mbambo, and A. St Clair Gibson. "Heart rate during training and competition for long-distance running." Journal of Sports Sciences 16 (1998): S85-S90. Print.
4. Palmer, G. Hawley, J.A., Dennis, S. and Noakes, T.D. (1994). Heart rate response during a 4 day cycle race. Medicine and Science in Sports and Exercise, 26, 1278-1283.
5. Plowman, Sharon A., and Denise L. Smith. Exercise physiology for health, fitness, and performance. 3rd ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2011. Print.
6. Selley, E.A., Kolbe, T., Van Zyl, C.G., Noakes, T.D. and Lambert, M.I. (1995). Running intensity as determined by heart rate is the same in fast and slow runners in both the 10- and 21-k, races. Journal of Sports Sciences, 13, 405-410.
7. Van Camp, S.P. (1998). Pharmacologic factors in exercise and exercise testing. In Resource Manual for Guidelines for Exercise Training and Prescription (edited by S.N. Blair, P. Painter, R.R. Pate, L.K. Smith and C.B. Taylor), pp. 135-152. Philadelphia, PA: Lea and Febiger.
8. Thomas, J.A. (1998). Drugs, Athletes and Physical Performance, pp. 217-234. New York: Plenum Press.
9. Wallace, J.: "Principles of cardiorespiratory endurance programming" In: Kaminsky, A. (ed.), ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription Fifth Edition. Philadelphia, PA: Lippincott Williams & Wilkins, 336-349 (2006).
10. Hamilton, M.T., Gonzales-Alonso, J., Montain, S.J. and Coyle, E.F. (1991). Fluid replacement and glucose infusion during exercise prevent cardiovascular drift. Journal of Applied Physiology, 71, 871-877.
11. Montain, S.J. and Coyle, E.F. (1992). Fluid ingestion during exercise increases skin blood flow independent of increases in blood volume. Journal of Applied Physiology, 73, 903-910.

Exercise Metabolic Systems Explainer

We get our energy from food and use that energy to perform work.  The carbohydrates, fats and proteins found in food are eventually converted into a molecule called ATP, the main energy source that allows humans to do work.  We get energy from ATP whenever this molecule loses one phosphate to become ADP.

There are three energy systems that we use to breakdown ATP which vary in dominance based on the intensity.  To determine which metabolic system is in dominance, especially with the lactic acid and aerobic system, heart rate monitors are often used to measure intensity.  Knowledge of heart rate training will allow the user to target specific metabolic systems to produce the desired training effect such as weight loss, reduced resting blood pressure, increased speed, power or overall endurance.  Many times, those with weight loss goals religiously train within the "fat burning" aerobic system and never get the results they want- this occurs mainly because the rate of energy burned is more important than the type of energy burned.  I will go into more detail about weight loss on a separate post.  (Remember that the energy systems don't operate independently, they all operate at the same time, but at different percentages based on the workout.)

1. ATP-Phosphocreatine Alactic Anaerobic System aka. ATP-PC or ATP-CP: Contributes to short-duration maximal exercises that require power.  This is a very important energy system to train if a sprint to the finish line is your strategy to the podium.
2. Lactic Acid "LA" system: This system is the dominant ATP manufacturer at the initial start of exercise (1-2 min), accelerations and any time pace is lifted.  It produces energy fast to sustain increased work demands.  Carbohydrate is the primary fuel source.  In racing, strategies called "attacks" or "accelerations" are used by competitive athletes to catch the competition off guard and force them to use CHO when it is least comfortable.  Athletes who can stay in this system longer are said to have a high lactic threshold.
3. Aerobic "O2" system:  The "cruise-control" system that dominates when the intensity is held at a steady state for (2-5 min).  Fat is the primary fuel source.  In racing, a strong aerobic system coupled with economy and consistency is an advantageous way to save glycogen stores for responses to attacks or to do the attacking.  This is a big reason why VO2max is one of the major contributing factor to success.

1. ATP-PC:

The ATP-PC system is similar to a recycling center because as ATP is broken down into ADP, PC almost instantaneously converts ADP back into ATP.  This system is often called "alactic anaerobic" because neither oxygen or lactic acid is produced.  Although hearing no lactic acid sounds like a dream come true, this system does have a time limit.  After a maximal muscle contraction, the ATP-PC system can only operate for about 10 seconds- it then loses efficiency almost entirely at 20 seconds (1).  

The ATP-PC system is dominant in muscle fibers that have a greater amount of PC compared to ATP.  In terms of muscle stores, there is about three times more PC compared to ATP (2).  Specifically, fast twitch muscle fibers have a greater ratio of PC to ATP compared to slow twitch muscle fibers.  This allows individuals who have a greater percentage of FT muscle fibers to excel in sports such as sprinting and jumping events.

2. Lactic Acid system:

When the ATP-PC system and the O2 system can't meet the energy requirements, the LA system takes over to quickly produce energy.  ATP is mainly produced through glycolysis and glycogenolysis.  Although this system can provide energy quickly, problems involve the rate of lactate production and lactate clearance.  If lactate production is greater than lactate clearance, lactic acid will accumulate and cause discomfort.

The LA system dominates at around one to two minutes of exercise; afterwards, the O2 system takes on more work to generate ATP.

How lactic acid is produced:

• In order for muscles to contract, calcium must be released from the sarcoplasmic recticulum.  Free calcium eventually activates an enzyme called glycogen phosphorylase, an enzyme that activates glycogenolysis- this process always results in the production of lactic acid with or without oxygen (3, 4).

• Enzyme activity and mitochondrial density.  Fast twitch muscle fibers have a greater concentration of the enzyme called lactic dehydrogenase.  This enzyme catalyzes pyruvate and NADH + H to produce lactate and NAD+.  As levels of NADH + H and pyruvate increases, so does the activity of this enzyme and the amount of lactic acid produced (5).

• Glycolysis.  As pyruvate is produced from glycolysis, it is reduced to lactic acid (6, 7,5).

• Stimulation of the sympathetic nervous system to release epinephrine and glucagon.  As a result of the breakdown of glycogen, a large amount of glucose-6-phosphate (G6P) is produced, a molecule that increases the rate of glycolysis and pyruvic acid.  The increased amount of pyruvic acid is then converted into lactic acid with the help of lactic dehydrogenase (6).

How lactic acid is cleared:

• Within the liver, lactic acid is converted into glucose through the process, gluconeogenesis.

• Gluconeogenesis also occurs within FT oxidative glycolytic and FT glycolytic muscle fibers.  Any lactic acid left over within the muscle enters gluconeogenesis to be converted back into glucose (3, 10, 9).

• Because of the normal PH level of the body, 99% of lactic acid is dissociated immediately into hydrogen protons and lactate anions (11).  Because lactate can pass easily through mitochondria, muscle, blood, active/ inactive muscles and skin, a small amount of lactic acid can pass through the skin with sweat (8).

2. Aerobic System:
ATP is generated through three processes: aerobic glycolysis, the Krebs cycle and the electon transport oxidative phosphorylation process.  The O2 system dominates after approximately two minutes of exercise.  Between one and two minutes, the O2 system and the anaerobic system produces approximately the same amount of ATP (1).  As exercise demands increase, oxygen consumption increases until reaching the maximum amount of oxygen that the O2 system can process.  The maximum amount of oxygen that the O2 system can consume is called the VO2 max.

Resources:
1. Gastin, P.B.: Energy system interaction and relative contribution during maximal exercise. Sports Medicine. 31(10):725-741 (2001).
2. Gollnick, P. D., & D. W. King: Energy release in the muscle cell. Medicine and science in Sports. 1(1):23-31 (1969).
3. Brooks, G.A., T.D. Fahey, T.P. White, & K.M. Baldwin: Exercise Physiology: Human Bioenergetics and Its Applications (3rd edition) Mountain View, CA: Mayfield (1999).
4. Fox, E.L.: Measurement of the maximal lactic (phosphagen) capacity in man. Medicine and Science in Sports (abstract). 5:66 (1973).
5. Spriet, L.L., R.A. Howlett, & G.J.F. Heigenhauser: An enzymatic approach to lactate production in human skeletal muscle during exercise. Medicine and Science in Sports and Exercise 32(4):756-763 (2000).
6. Brooks, G. A.: The lactate shuttle during exercise and recovery. Medicine and Science in Sports and Exercise. 18(3):360-368 (1986).
7. Gasser, G.A., & G.A. Brooks: Muscular efficiency during steady-rate exercise: Effects of speed and work rate. Journal of Applied Physiology. 38(6):1132-1139 (1975).
8. Brooks, G.A.: Intra- and extra-cellular lactate shuttles. Medicine and Science in Sports and Exercise. 32(4):790-700 (2000).
9. Gladden, L.B.: Muscle as a consumer of lactate. Medicine and Science in Sports and Exercise. 32(4):764-771 (2000).
10. Donovan, C.M. & M.J. Pagliassotti: Quantitative assessment of pathways for lactate disposal in skeletal muscle fiber types. Medicine and Science in Sports and Exercise. 32(4):772-777 (2000).
11. Gladden, L.B.: Lactate metabolism: A new paradigm for the third millennium. Journal of Physiology. 558:5-30 (2004).

High-Intensity Interval Training (HIIT) Timer

Typically, an interval timer may costs anywhere from $15 to $100+.  Now, interval timers are free as long as you have a smart phone.  There are a lot of interval timer apps on the android market, but many of them either have an obnoxious alarm or fail to alarm if the work and rest intervals are set to 3 and two seconds, respectively.  Short intervals are important for targeting eccentric or concentric muscle contractions to produce the appropriate training effect.  I was surprised to find that this timer could function even if the interval was set to the shortest possible duration (1s work/ 1s rest).

To get the same app, search "hiit interval training timer" on the android market and download the app with the square icon, silhouette of a runner and the letters "HIIT" underneath the trailing leg of the runner.

PROS:

• It's free!

• Easy to use

• No obnoxious alarm at the end of each timer

• Loud enough to hear outdoors while running or cycling

• App can operate in the background

CONS:

• App interface could look better... can't really complain since it's free!

Lezyne Alloy Floor Drive Pump Review

Updated 8.5.2024

It has been thirteen years and I'm still using this pump!  I replaced the gauge and pump head only because I needed to read higher pressures for my suspension post.  Otherwise, this pump has been completely reliable, and I haven't needed to replace any wear and tear items yet.  Kudos to Lezyne for not practicing planned obsolescence!

Compared to pumps at the same price range, this pump doesn't have proprietary parts; instead, it uses standard O-rings which can be found in virtually any hardware store.  That's mainly what motivated this purchase.


PUMPING EFFORT:
This pump feels very solid and will pump a bicycle tire very fast.  Although it takes time to attach the threaded chuck to the valve, it creates a better seal and guarantees that the valve won't be damaged. On average, it takes one minute to pump both tires.

Edit 8.5.24:  I swapped to the dual pump head with the flip, lock lever, and it has made pumping even faster!


EASY TO USE DESIGN:
Lezyne did a great job with designing this pump so that it would be easy to use and transport.  The hose is about four feet long and slots into the harness located at the base.  The 2.5 inch gauge was easy to read and it was surprisingly more accurate than I expected.  When compared to my dedicated pressure gauge, this pump was within 5 psi of the actual pressure.  Considering that other pumps are usually 15-20 psi off, this is pretty good!  If you have bikes with Presta and Schrader valves, all you have to do is unscrew, and flip the chuck to switch between each valve type.


TIPS FOR THREADED CHUCKS:
If you're new to using threaded chucks, you will probably lose a lot of air as you unscrew the chuck.  To get around this problem, just overinflate the tire 15-20 psi above your target to leave room for error.  You will also want to leave enough room to fine tune the tire pressure with a separate tire pressure gauge.  You'll always lose some air inside a gauge.

PROS:

• Extremely easy to pump from zero to 250 psi (suspension tuning)

• Chuck fits onto presta and schrader valves

• Threaded chuck is leak proof and won't damage your valve

• The replacement parts are easy to find and inexpensive to replace

• Nearly 4 foot long hose

• Fairly accurate gauge +/- 5 psi

CONS:

• $70 for a pump is a lot to dish out. But in this case, it's the last pump you'd ever need since repairing it is easy and convenient.

• Looks too nice to get dirty- you'll want to wash your hands before touching the wood handles

• If you're new to threaded chucks, you will be annoyed during your first dozen attempts of trying to get the pressure right.  Practice!