Here's an interesting read by Tom Venuto:
This subject definitely calls for a closer examination because definitions of "full range" are fuzzy and although using full range of motion when lifting weights is generally good advice, it is not set in stone. In fact, there are circumstances where "full range" can be taken too far and where using a partial range has decided advantages.
Defining Full Range of Motion
The first thing we need to do is define what full range of motion means. Sometimes the full range of an exercise is clear. For example, a bench press full range of motion is to lower the bar from the fully extended (arms-length over the chest) position down until the bar touches your chest.
In other exercises, full range of motion is not so clearly defined. For example, in the squat, the exercise begins with you standing up, but how low should you go? Most people define full range as squatting down to parallel, but others say you should break parallel ("full" squats). Who is correct? In some cases, full range of motion is a matter of opinion.
Range of Motion: Exercises Versus Muscles
It's also important to point out that the full range of motion of a muscle and the full range of motion of an exercise are not the same thing. In the barbell bench press, the exercise ends when the bar is lowered until it hits your chest. That's full range of motion for the exercise. But that's not the full range of motion for the pectoral muscles. If you used dumbbells, the range of motion could be greater, as you could extend the range by dropping the dumbbells further into the stretch position.
A muscle's full range of motion is the distance between full extension and full flexion (stretched and contracted position). In other words - as far as your muscles and joints allow you to move. However, in many cases, if you could use this full range of motion under heavy resistance during a weight training exercise, it might actually make you more prone to injury.
Dangers of Using an Exaggerated Range of Motion
Many bodybuilders over-emphasize the stretch position to achieve a "greater range of motion," hoping that this will recruit the pectoral muscle fibers more thoroughly. Unfortunately, what it may also do is overstretch the pectorals while under resistance, increasing the odds of shoulder joint damage or even pec tears.
In this sense, taking range of motion too far is not a wise thing to do. Some trainers recommend testing the amount of flexibility you have in your shoulder joint to determine the proper range of motion. Known as the "passive" shoulder range of motion, this is the point where your arm naturally stops without being forced or pushed. In the bench press, if you are tight, this might fall short of the point where the bar touches your chest.
For people who have joint pain or injuries, and or who have poor flexibility, limiting the range of motion slightly on certain exercises helps reduce strain on the joint. An observer might think you are cheating or using bad form because you're not lowering the bar all the way to your chest, but what you're really doing is saving your shoulders.
There are other exercises where the full range of motion concept can also be taken too far. In the leg press, for example, you could lower your knees until the point where they are literally hitting your chest. At this point however, most people have rolled their butt off the seat, causing a posterior pelvic tilt. This puts an enormous strain on the lower back. It's safest to end the eccentric part of the rep just before your hips roll back off the seat. That is the correct (and safe) full range of motion, even though its possible to go further.
Beneficial Uses For Partial Range of Motion: Bodybuilding
I agree for the most part, with the conventional wisdom that your default method should be to perform your reps through the exercise's full range of motion, most of the time. However, as the examples above demonstrate, this rule is not carved in stone. Beyond the safety considerations mentioned above, there are some situations where using less than full range of motion could be beneficial for muscle growth.
There is a technique in bodybuilding called "continuous tension", where an exercise is performed through almost the full range of motion, but stops just shy of locking out the joint. For example, on shoulder press (military press) you wouldn't lock out your elbows out 100%, you would keep just a slight bend in the elbows at the top.
This method is used on exercises where there is LESS tension on the muscle in the lockout positions - usually pressing and pushing. Some exercises and machines (notably cables) maintain tension / resistance at the fully extended position so it's actually more beneficial NOT to cut the range short. The idea is not a shorter range of motion per se, but to seek out the path of most resistance and avoid "dead spots" where there is little or no resistance. This is why some machine companies have created machines with variable resistance cams
This type of partial range training does not allow the muscle to relax - it keeps the primary movers under contraction continuously. It also produces an occlusion effect, trapping blood in the muscle and creating a greater pump than normal. In addition, exercises like shoulder presses are compound movements, involving the triceps heavily at the top lockout position. But what if you want to reduce tricep involvement and focus on the deltoids more? In this case, excluding the top lockout portion makes sense.
I wouldn't consider it bad form to stop just short of lockout for hypertrophy/ bodybuilding training. In fact, considering that strength development carries over to as much as 20 degrees beyond the training angle (Graves 1989), if you do almost full range repetitions, your strength development should be approximately equal to a full rep.
When training for bodybuilding / hypertrophy, this non-lockout, continuous tension technique is very effective - and very challenging. It will feel much more difficult because the muscles do not get a chance to rest between repetitions. Plus, the lactic acid buildup is more noticeable and sometimes creates a very intense burn.
Continuous tension training for bodybuilding will limit the amount of weight you use somewhat due to fatigue buildup and zero rest / pause between repetitions due to lockout, so again, it is a superior method for muscle size but usually not quite as effective for lifting maximum poundage or developing maximum strength. However, there is another use of partial range repetitions that is used often by advanced strength and powerlifters.
Beneficial Uses For Partial Range of Motion: Strength and Powerlifting
It's well known that your strength can vary throughout the range of motion of a given joint. This is due to the length of the lever arm, the muscle length-tension relationship, muscle mass and muscle activation. The different amounts of strength you have at various points in an exercise is known as the "strength curve." Understanding this curve allows exercise scientists and strength coaches to identify the area where each lifter has the highest amount of force output.
The strongest range of motion is usually in the upper portion of the lift, 2 to 5 inches from the completion of a repetition. This has prompted many powerlifters, bodybuilders and strength athletes to train with maximal or even supra-maximal weights (heavier than 1 rep max for full range reps) in the strongest range of motion.
Vladimir Zatsiorsky, the famed sports bio-mechanics expert and former strength and conditioning coach for the Soviet Union Olympic Teams, called this method Accentuation. He proposed that one should train strength in "the range of the sport movement where the demand for high force production is maximal." The idea is that adaptations should occur due to the extreme overload and from a decline in neural inhibition.
In a study from Bloomsburg University (my Alma mater), Mookerjee and Ratamess found that the use of partial repetitions increased performance significantly for both the 1 rep max and the 5 rep max. They hypothesized that the improvement might have occurred due to a motor learning response and improved coordination of primary and stabilizing muscles. They also mentioned that this technique can be a useful method for advanced-level strength athletes to overcome plateaus.
At the University of Mississippi a study was conducted in 2004 by C Dwayne Massey and his team to confirm the partial range of motion theory. 56 subjects were divided into 3 groups. Group one performed the bench press for 3 full range of motion sets. Group two performed the bench press for 3 sets of partials, defined as the range of motion 2 to 5 inches from lockout. Group 3 trained with a combination of partials and full range reps
After 10 weeks of training, no differences in strength were found between the 3 groups. While neither method proved superior, Massey noted that the partials technique "would appear to be of benefit to powerlifters as they attempt to lock out a weight at the top of the lift and similarly for athletes who must demonstrate strength in the upper portion of their range of motion."
In a second study in 2005 from the same lab, Massey's team used a similar test protocol with female subjects. This time, once again, all groups increased strength, but the group that used the full range of motion increased strength the most. The female subjects in this study were college students and were relatively inexperienced lifters. It's likely that more advanced lifters may be able to benefit more from the use of the partials technique.
More research with both genders at all levels of training experience is needed to make firm conclusions about the partials technique. However, there are at least five studies that suggest using partials can positively influence the development of maximal strength and experienced strength athletes can confidently include this method as an adjunct to their normal training protocols.
Intelligent use of partials versus bad form
In contrast to the use of partial range of motion (not locking out) for bodybuilding or using top range partials ("lockouts") for breaking through sticking points and strength plateaus, what you often witness in the gym is flat-out bad form. Someone loads too much weight on the bar or machine, and performs a partial repetition simply because the weight is too heavy to perform a proper full rep so they only complete the range of motion they can with such a weight.
The most common examples of this bad form error are seen in the leg press and squat. On either exercise, the top quarter or so of the range of motion is the easiest part because that's where you are the strongest (the deeper you go, the harder it gets). So the trainee puts too much weight on the bar and can only lower the weight a quarter or half the way down. If he were to go any deeper, he would get stuck at the bottom.
It's one thing to intentionally restrict the range of motion as a bodybuilding or strength technique - it's another (and it IS bad form) to add more weight than you can handle properly and restrict range of motion for that reason. This is often nothing more than "ego lifting" and it can also be very dangerous. The compressional forces on the spine are increased greatly with the type of heavy loads that can be used on top range quarter reps and getting caught at the bottom of a squat or any heavy lift is no laughing matter.
Conclusions and Recommendations
As a "best practice," perform the majority of your exercises through the full range of motion given your level of flexibility and orthopedic conditions. Occasionally use partials, continuous tension, burns and other techniques as appropriate to your goals and your need for variety in your program. Train hard, and above all train smart and train safe.
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References
Graves JE, et al. Specificity of Limited Range of Motion Variable resistance training. Medicine and Science in Sports and Exercise. 21(1) pp 84 - 89. 1989. University of Florida, Gainesville FL.
Massey CD et al. Influence of range of motion in resistance training in women: early adaptations. Massey CD et al, Journal of Strength and Conditioning Research. 19(2) pp 409-411. 2005. University of Southern Mississippi
Massey CD et alAn analysis of full range of motion vs partial range of motion training in the development of strength in untrained men. Journal of Strength and Conditioning Research. 18(3) pp 518-521. 2004. University of Southern Mississippi
Mookerjee S. and Ratamess N, Comparison of Strength Differences and Joint Action Durations Between Full and Partial Range of Motion Bench Press Exercise. Journal of Strength and Conditioning Research. 13(1) pp 76-81. 1999. Exercise Physiology Laboratory, Bloomsburg University.
Zatsiorsky, Vladimir.Science and Practice of Strength Training. Human Kinetics Publishing, Champaign, IL. 1995