Body Fat... Why Measure It?

There are two good reasons to measure body composition.  It provides an objective way to track progress towards better health or fitness, and it directly affects performance.

Fat cells aka adipocytes (above) store lipids in two ways.  White fat cells store lipids in one giant mass, and brown fat cells store lipids in groups of many little sizes. Humans carry more WFC's than  BFC's (5).

ASSESS TO PREVENT OBESITY:
There are short term and long term changes that a fat cell can undergo.  Think of the fat cell as a balloon that duplicates itself after reaching its maximum size.  When fat intake rises, the first physiological change that occurs is an increase in size (up to 10x larger) caused by the storage of lipids (3).  This is a short term change which can be restored through dietary and exercise interventions.  If nothing is done to reduce the amount of lipids stored in each fat cell, eventually the fat cell will undergo cell division as well as the maturation of precursor cells to fat cells (2,3).  Basically, you'll end up with more fat cells than you started with.  Generally, someone with a normal percentage of body fat has about 30 to 50 billion fat cells whereas an obese individual can have 75-80 billion fat cells (3).

After the original fat cell undergoes hypertrophy (enlargement), it remains the same size even when emptied.

If the new fat cells have time to mature, they will also (permanently) remain the same size despite a significant loss of body fat (4).  In other words, the balloons will deflate, but they'll remain on standby;  eagerly waiting to store more fat.  This is a major reason why obese people who successfully loses weight cannot maintain the weight loss.  This is why body composition tracking is extremely important.

BODY COMPOSITION TESTING BENEFITS EVERYONE:
Just as important as it is to prevent excess body fat, it's also important to prevent body fat from getting too low.  Young women and athletes who benefit from a low body weight are particularly at risk for eating disorders (1).  Pay attention to the fine line between attention and obsession with regards to body weight or composition.

Changing body composition affects the metabolic systems.  If less fat is available to use as energy, more carbohydrates will be fed into the LA system.  The goal for endurance sports is to primarily use fat, and save carbs for the harder parts of a race.

Because the relative proportion of bone, muscle and fat are directly affected by changing body composition, performance may decrease due to a shift from homeostasis or equilibrium.  Remember that both anaerobic and aerobic metabolic systems are used simultaneously, but at different percentages.  Because the mitochondria are located in fat and muscle, reducing fat mass will leave the mitochondria with less accessible fat to use as energy.  With a healthy diet, the body will naturally take on the optimal body fat percentage.

WHO BENEFITS THE MOST FROM REGULAR BONE DENSITY TESTING?  The older population benefits the most, especially those who are at a higher risk of falling.  Early detection helps determine if the current regimen of exercise, nutrition, and supplementation is adequate.  Surprisingly, road cyclists, including professional cyclists, also have a high risk of developing sarcopenia or below normal bone density.

THE SEVEN WAYS TO MEASURE BODY FAT:

There are six popular ways to measure body fat.  I ranked the assessments based on most accurate (#1) to least accurate (#6).

• Body Fat Assessment #1: Hydrostatic weighing
• Body Fat Assessment #2: Skinfold Meaurements
• Body Fat Assessment #3: Bioelectrical Impedance
• Body Fat Assessment #4: Body Circumference
• Body Fat Assessment #5: Waist to Hip / Waist Circumference
• Body Fat Assessment #6: Body Mass Index "BMI

REFERENCES:

1. Kaminsky, Leonard A..ACSM's health-related physical fitness assessment manual. 3rd ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins Health, 2010. Print.
2. Malina, R. M., C. Bouchard, O. Bar-Or (2nd ed.): Growth,  Maturation and Physical Activity. Champaign, IL: Human Kinetics (2004).
3. 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.
4. Sjöström, L., & P. Björntorp: Body composition and adipose tissue cellularity in human obesity. Acta Medica Scandinavica. 195:201–211 (1974)
5. Malina, R. M., C. Bouchard & O. Bar-Or: Growth, Mat-uration and Physical Activity (2nd ed.) Champaign, IL: Human Kinetics, 163 (2004). Reprinted by permission.

Body Fat Assessment #3: Bioelectrical Impedence

WHAT IS IT?
Bioelectrical Impedance or BIA is an indirect method of determining body fat percentage by measuring the amount of resistance the body provides when a current of electricity is passed through the body.  A high or low resistance corresponds to a high or low body fat percentagE, respectively.

HOW IS IT DIFFERENT?
Compared to other methods, this is the least invasive and most comfortable way to assess body fat.  Unlike other methods where they are only effective if the individual wears short running shorts with no shirt, the only body parts that need to be exposed with BIA are the hands and the feet.  The BIA machine I used involved only two pairs of electrodes which needed to be placed on my right hand and foot; afterwards, all I needed to do was lie down supine (on my back) and relax while the machine did all of the work.  Very easy and less painful than the deep folds that need to be pinched for skinfold measurements.  While I'm on the subject of pain, it's also worth mentioning that BIA doesn't hurt and is in fact, the electrical current is so weak that it is unnoticeable- only the machine itself can detect the current.  The only thing I found painful was removing the electrodes and some of my hair at the same time.  This is still less painful than the pinching and pulling required for skinfold measurements.

LIMITATIONS & SOLUTIONS:
In terms of comfort, invasiveness, convenience and ease of execution, BIA is a great assessment to use.  Its only flaw involves a few conditions where its accuracy may become questionable.

• Limitation #1 - Hydration Affects BIA:  Because electrical currents may become affected by water and electrolyte levels, the individual's hydration and nutritional status must be kept within normal limits to get more accurate results.  Too much water would theoretically decrease resistance and the body fat percentage; although studies have also found the opposite to occur in two conditions: During exercise and after consuming a large quantity of sport drinks (3).  I'm not sure why anyone would do either during a BIA test though...
• SOLUTION:  To get around this problem, it is recommended that the BIA be done three to four hours after a meal or an exercise session (3).
• Limitation #2 - Ambient and Skin Temperatures Affects Resistance: When the temperature of the testing area is cool, resistance will be higher- the opposite is true for hot temperatures (2,4).  This same relationship also holds true for hot and cold skin temperatures (2,4).
• SOLUTION:  If you're going to take a BIA measurement, make sure the room has a neutral temperature of 27-29 degrees Celcius or 80-84 degrees Fahrenheit (3).  Also make sure that you are neither overheated or chilly.  Get to the assessment on time so that you won't have to literally run or speed walk to make it in on time- even a quick sprint will cause skin temperatures to rise quickly.  If it is cold outside, dress appropriately so that your skin temperatures adjust more quickly to the temperature of the room.
• Limitation #3 - BIA Equations Vary By Make/ Model of Machine: Don't get angry if the measurement taken at your first assessment does not agree with the measurements you received at new place.  Because there isn't a universal equation available for BIA, the manufacturer must "tailor-fit" their equation to match their machine.
• SOLUTION:  There really isn't a way to get around this but to try to find a new place that uses the same BIA equipment.
• Limitation #4 - Inaccurate on Individuals with Normal %BF:  Due to a combination of the above limitations, BIA cannot accurately measure individuals who are not at the extreme of leanness or obesity.
• SOLUTION:  According to a study, although BIA is accurate under standard conditions, BIA is probably no better than skinfolds (1).  So if accuracy is top priority, it might be wise to stick with skinfolds from the start to avoid headaches in the future.  This is the final limit of BIA where it is basically useless as a way to track progression.  The best method at this point is to use skinfold measurements to track where fat is being stored at specific sites in the body.

REFERENCES:

1. Baumgartner, R.N., W.C. Chaunlea, & A.F. Roche: Bioelectrical impedance for body composition. In K.B. Pandolf (ed.), Exercise and Sport Sciences Reviews. Baltimore, MD: Williams & Wilkins, 18: 193-224 (1990).
2. Caton, J.R., P.A. Mole, W.C. Adams, & D.S. Heustis: Body composition analysis by bioelectrical impedance: Effect of skin temperature. Medicine and Science in Sports and Exercise. 20(5):489-491 (1988).
3. 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.
4. Stump, C.S., L.B. Hourkooper, M.H. Hewein, S.B. Going, & T.G. Lohman: Bioelectrical impedance varability with dehydration and exercise. Medicine and Science in Sports and Exercise. 20(2):S82 (1988).

Training Program Design Breakdown

For any experienced fitness professional, the following principles should be a good review to make sure the training program is designed correctly.  If the following training principles sound new, applying these principles will definitely make a positive change to any program.

1. SAID Principle:  SAID stands for "specific adaptations to imposed demands" which means that what you do is what you get.  All training programs should be specific to the goal of the individual.  Does the individual need to work on strength, power, cardiorespiratory endurance, flexibility, mobility, agility or muscular endurance?  For example, a sprinter would not necessarily benefit from a program that focuses mainly on long distance running to improve muscular endurance.  A sprinter would need a program that focuses on strengh, power, flexibility and mobility.  After determining what component to work on, the metabolic demands of the activity must be known.  Does the activity require a lot of ATP-PC activity or more on the lactic acid and aerobic metabolic systems?  Finally, the movements used in strength training must also resemble the movements of the sport or activity.  For cyclists, they would benefit more from a plyometric squat (concentric phase only) than a plyometric split squat because the split squat fails to resemble the movement of the legs and feet on the pedals.  The closer the training program imitates the specific activity or sport, the chances are better that the program will produce positive results.
2. Overload:  The overload principle refers to the amount stress placed on the body.  For a positive training effect, the overload needs to be greater than what the body is used to.  For example, performing a work interval at a recovery intensity is a good way to progress no where.  There are four ways to provide overload.  Frequency, duration, intensity and volume can all be changed to make the exercise program more or less challenging.
• Frequency is the number of sessions trained per week.  By including 24 hours of rest in between session days, the max a beginner can train in a week is four days- a good reason to never miss a workout!  Once a strong athletic base has been built, seven days a week is possible with more opportunities to skip workouts if needed.
• Duration is the length of time spent on the workout(s).  There is usually an inverse relationship between duration an intensity.  As duration goes up, intensity usually goes down, vice versa.
• Intensity is the amount of effort required by the session.  This can be measured with a heart rate monitor, RPE or as a percentage of the maximal amount of weight an individual can lift for one repetition (1RM).  In aerobic exercise, intensity is often determined through percentages of maximum heart rate or target heart rates.
• Training volume is the total time spent exercising throughout the week and may be calculated by multiplying frequency by duration (3).  For example, training 7 days per week for 30 minutes every workout has a training volume of 210 minutes per week.  On the other hand, training 4 days a week for two hours every workout yields a training volume of 480 minutes.  It is important to be aware how much volume was designed into the program.  Overtraining and overuse injuries may occur by failing to pay attention to the rise in training volume.
3. Recovery:  To balance the principle of overload, the principle of recovery is absolutely necessary for allowing the body to recover and adapt to the demands it experienced after the training session or work interval.  Without a recovery period, the body will accumulate more damage than repair- a recipe for injury.  By allowing the body to repair damaged muscles/ fascia and replenish energy stores, this will ensure that the next training session can be performed at the same intensity or higher- better yet, there will also be a reduced risk of injury.  No pain, big gains!
4. Progression:  The amount of overload and recovery may change throughout a training cycle.  Progression is a way to determine if the program has too much or too little of overload or recovery.  The steploading method used commonly in periodized programs produces optimal progression (1,2).  In steploading, training load is progressively increased until every third of fourth session where the training load is decreased to allow for recovery and adaptations (1,2).
5. Variability/ Reversibility:  As the individual progresses throughout the training cycle, progression may begin to occur more slowly until a plateau is reached.  Once a plateau is evident, confirm whether or not the cause of the plateau is due to overtraining.  The principle of variability emphasizes the importance of varying the type of overload used in training.  In other words, try to avoid doing one type of exercise.  For example, competitive cyclists need strength, power, flexibility and endurance to become faster.  If the cyclist's program only focuses on bike-only exercises, a plateau will definitely occur as well as an increased risk of overuse injuries.  Although bike work is important, strength training and flexibility is key to preventing injury and correcting muscular imbalances caused by cycling.
6. Maintenance:  Once the desired level of fitness is achieved, maintenance becomes the main goal to ensure that the adaptations gained through training is not lost.  In order to maintain a level of fitness, intensity must be maintained.  Duration and frequency may decrease without losing the positive adaptations; although the amount of the decrease depends largely on the individual (3).  For most endurance athletes, a rapid loss of cardiorespiratory endurance can be prevented with a minimum of three sessions per week at 75% VO2 max (4).
7. Individualization:  Because of differences in gender, age, diseases, genetics, body type, stress, diet and amount of sleep, not everyone will adapt the same way to a training program.  With that being said, never use the same exact "one size fits all" program for everyone!  Some people may overtrain, plateau or even detrain to a same program.
8. Warm Up & Cool Down:  Like the SAID principle, the warm up and cool down must be specific to main exercise of the session.  For example, before a hard cycling interval on an upright bike, the cyclists should warm up preferable on an upright bicycle rather than a recumbent bicycle.

References:

1. Bompa, T.O.: Periodization: Theory and Methodology of Training. Champaign, IL: Human Kinetics (1999).
2. Freeman, W.H.: Peak When It Counts: Periodization for American Track & Field (3re edition). Mountain View, CA: Tafnews Press (1996).
3. 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.
4. Mickelborough, Timothy. "Training for Sport." Exercise Physiology. Health Physical Education and Recreation. Indiana University Bloomington, Bloomington. 10 Aug. 2010. Lecture.

What is the Core?

In an adult skeleton, there are about 206 bones (1).  Of the 206 bones, only five of them serve as an important skeletal structure that the core muscles press and pull against.  Unlike the thoracic spine, the five disks of the lumbar spine does not have ribs that provide it with additional strength, stability for posture, shock absorption and rigidity against impact.  To overcome this obstacle, the body has to rely on a network of muscles and fascia to take on the demands that both bone and muscle experience, this is the core.  Because the muscles of the core can move the spine through all planes of motion, the lumbar spine is more vulnerable to damage.  Any muscular imbalance will cause the spine to favor a dangerous posture and likely damage the lower back.


THE IMPORTANCE OF MUSCLE BALANCE:
The relationship between the muscles of the lumbar spine and the disks can be best interpreted as a guy wire system.  Imagine that the lumbar spine is a five story tower with muscles or "wires" that attach to both sides.  In normal conditions (see figure 1.1), the muscles of the lumbar spine keep the disks aligned correctly- both sides have equal tension.  In unhealthy conditions (see figure 1.2), the disks are pulled out of alignment due to unbalanced muscular strength. As shown on figure 1.2, the wires to the right overpowered the wires to the left and caused the tower to lean out of alignment.  In muscular terms, the wires to the right are now in a tightened position and the wires to the left are in a stretched position.  If no actions are taken to correct this imbalance, low back pain will usually occur.

Figure 1.2 Unbalanced

Figure 1.1 Balanced

Muscular imbalances may be caused by the following:

1. Poor posture for extended periods of time
• Example:  Driving, office jobs, watching tv, sitting at a table and waiting at an airport
2. Poor posture while lifting light or heavy objects
• Example:  Prepping and cooking food, reaching for objects above shoulder height, moving boxes and lifting suitcases/ luggage
3. Repetitive activities/ sports dominantly in one plane of motion.
• Example:  Running, cycling, swimming and rowing.
4. Poor posture during sports
5. Poorly designed weight lifting programs. 
• Example:  Only performing exercises to visibly improve rectus abdominis appearance ("six pack").

ANATOMY & FUNCTION OF THE CORE:
There is more to the core than the "six pack" muscle, the rectus abdominis.  In addition to the diaphragm and the muscles of the pelvic floor, there are about 16 muscles- a lot more than this if I were to include every intricate muscle.  If you feel comfortable with the anatomy of the core, skip onto the next section about core exercise design.


Starting with the deepest groups of muscles, there are eight muscles that directly affect the movement of the lumbar spine.  The first group of muscles is the erector spinae group.  This group is responsible for spinal extension and posture.  The second group of muscles is less well known probably because the name is not as easy to remember, the transversospinalis group.  These muscles are small and literally attach from vertebrae to vertebrae.  Their purpose is to provide stabilization of individual vertebrae and prevent excessive rotation, lateral flexion and spinal flexion.  The quadratus lumborum is in a group of its own because it is able to perform two entirely different movements of the spine, spinal extension and lateral flexion.  Through bilateral (at the same time) contractions, this muscle performs spinal extension.  If used unilaterally (one side only), the quadratus lumborum laterally flexes the spinal column and also lifts the hip upward. (4)


Due to its function, the middle layer is usually the most important core muscle group to focus on.  As a group, the muscles/ fascia form a box.  This layer is important because it contains the transverse abdominis, the muscle responsible for providing the compressive forces that takes off stress from the lumbar spine and provides a stable foundation for the upper and lower body to press and pull against.  If the transverse abdominis is weak, more stress is placed on the lumbar spine and the muscles of the extremity will have to work extra hard.  Why is this a problem?  In addition to the risk of low back pain, the increased demands on the extremities means that more stress will be placed on the joints above and below the core.


The outermost layer of the core is responsible for gross movement of the trunk and also provides additional compression.  This group consists of the rectus abdominis, internal oblique, external oblique, latissimus dorsi and the iliopsoas (hip flexor).

Deep layer:

• Erector Spinae - Spinal extension

• Iliocostalis, longissimus and spinalis

• Transversospinalis - Spinal extension, lateral flexion of the spine, rotation of the spine

• Interspinalis, Intertransversarii, multifidus, rotatores and the semispinalis group (thoracic) 

• Quadratus lumborum - Bilateral activation = spinal extension , Unilateral activation = lateral flexion of the spine

Middle layer (the box):

• Diaphragm - "The lid"

• Pelvic floor - "The bottom"

• The sides of the box

• Transverse abdominis - Flexes vertebral column/ compresses abdominal wall

• Quadratus lumborum - Spinal extension/ lateral flexion of the spine

• Multifidus - Spinal extension, rotates spinal column

Outermost layer:

• Rectus abdominis (connected by linea alba) - Spinal flexion, compresses abdominal wall and helps with expiration

• External oblique

• Bilateral - Spinal flexion & compresses abdominal wall

• Unilateral - Lateral flexion of the spine

• Internal oblique

• Bilateral - Spinal flexion & compresses abdominal wall

• Unilateral - Lateral flexion of the spine

• Iliopsoas

• Bilateral - Spinal flexion

• Unilateral - Lateral flexion of the spine

• Latissimus dorsi (Thoracolummbar Fascia)

FOUNDATION OF CORE EXERCISE DESIGN:

By knowing that the core is a group of muscles that works as one unit to stabilize the abdominal area, it is easier to understand why crunches and sit-ups are not effective core exercises.  These exercises target mainly one muscle rather than all of the core muscles at once.  Choose exercises that will make the core work hard to keep the spine positioned correctly.  Because core exercises directly affects the spine, risk of injury is greater; so be sure to consult a fitness professional to ensure that the exercises are performed with correct form.


Core Exercise Tip #1:  Learn how to activate the core and breathe at the same time.
If you noticed above, the majority of the core muscles are responsible for compressing the abdominal wall to provide a stable foundation.  This means that any exercise can become a core exercise as long as core activation is learned.  There are two methods that many use to activate the core, abdominal hollowing and bracing.  McGill stated that in terms of stabilizing the spine, bracing was more effective than abdominal hollowing or "centering", a common method used for yoga/ pilates (3).  Another study also found that bracing was a more effective method to stabilize the spine (2).  In order to brace effectively, I always pretend as if I was about to be punched from the front, sides and back of my abdominal wall at the same time.  While activating the core, remember to always breathe or else blood pressure will rise very fast!


Core Exercise Tip #2:  Choose exercises that require core activation to stabilize the spine throughout all planes of motion.
Because the core is responsible for maintaining good posture by preventing movements such as spinal flexion, extension, rotation and lateral flexion at the spine, it is important to challenge the core this way.  Exercises such as the half kneeling anti rotation is an excellent way to challenge the core through rotational forces.  To challenge the core in the sagittal plane, a popular exercise is the plank and variations on it.  To prevent lateral flexion at the spine, the farmer's walk is an excellent choice.


Core Exercise Tip #3:  Don't forget the lats!

Although it seems like it doesn't belong, the latissimus dorsi contributes to the stability of the core.  Because the lats are located at the core, they will provide additional stability for the deeper muscles to press against.

Resources:

1. 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.
2. Gambetta, V. (2007). Athletic Development: The Art and Science of Functional Sports Conditioning. Champaign, Ill.: Human Kinetics
3. McGill, S.M. et al. (2003). Coordination of muscle activity to assure stability of the lumbar spine. Journal of Electromyography and Kinesiology, 13, 353-359.
4. McKinley, Michael P., and Valerie Dean Loughlin. Human anatomy. Boston: Mcgraw-Hill Higher Education, 2006. Print.

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.