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o provide an informed comparison of free weights and selectorized machines it is first necessary to have an explicit understanding of their purpose - both what it is and how it is best accomplished The reason for the numerous misconceptions that exist surrounding the subject is that the majority of people claiming expertise and making authoritative statements on the issue lack this understanding as well as understanding of related concepts such as motor learning and skill transfer and basic mechanical physics [http://www.rowlettmovers.com/ Rowlett Moving Company] It is important to note that there are currently over fifty companies manufacturing a wide variety of selectorized machines and the overwhelming majority of these are incorrectly designed This article is only concerned with properly designed machines The purpose of performing an exercise is to fatigue or inroad the strength levels of the involved muscular structures to a meaningful degree to stimulate a growth mechanism Ideally this should occur within some minimum time frame to avoid using any more of the body's limited metabolic resources than necessary since those same resources are required for recovery and growth There are a variety of factors which affect how efficiently an exercise accomplishes this Some of these include how well the resistance is balanced to the users strength in different positions over the range of motion whether the targeted musculature is loaded directly and how well the exercise facilitates focus and concentration on the targeted musculature Variable Resistance A person's usable strength changes from position to position during any movement due to the effects of friction myofibril congestion virtual cam effects resulting from the changes in tendon insertion angles and other factors as well as changes in leverage resulting from the changing angles of the involved bones during multi-joint movements If we graph these changes in usable strength over the full range of motion of any particular exercise we have what is referred to as the strength curve for that exercise The resistance provided by free weights or machines can also vary over the range of motion of an exercise due to changes in leverage or torque This change in resistance over the range of motion is what is referred to as the resistance curve for that exercise Ideally this resistance should vary in proportion to the strength curve of the involved muscular structures increasing in positions where they are stronger and decreasing in positions where they are weaker This makes it possible to meaningfully load the muscles continuously throughout the exercise and achieve the desired level of inroad with little or no energy wasted The less wasted during exercise the more available to the body afterwards for recovery and growth [http://www.rowlettmovers.com/ Rowlett Moving Company] In free weight exercises involving rotation around a single joint such as barbell curls dumbbell lateral raises and dumbbell chest flies the resistance curve resulting from the change in torque over the range of motion matches a portion of a sinusoidal curve see figure A below This does not match the strength curve for most rotary movements however which require an exponential decrease in resistance towards the end of the range of motion see figure B below While some free weight exercises can be performed in a manner in which the resulting resistance curve more closely approximates the strength curve of the involved muscles perfect congruence is difficult if not impossible to accomplish Figure A - The resistance curve resulting from the strict performance of a barbell curl If the resistance provided by an exercise does not vary in proportion to the strength curve the amount of weight that can be used is limited to how much one is capable of handling in the position where the resistance is greatest This is commonly known as the sticking point in free weight exercises As a result the involved muscular structures are only meaningfully loaded over a small portion of the range of motion of the exercise During the rest of the exercise the relatively lower resistance allows the muscles a respite during which some motor units may recover more than if the muscles encountered meaningful resistance over the full range of motion This reduces the rate of inroad resulting in less efficient growth stimulation In a properly designed machine a cam or system of levers varies the resistance over the full range of motion in proportion to the strength curve of the involved muscles increasing it in positions where the muscles are stronger and decreasing it in positions where they are weaker This provides continuously meaningful loading during the exercise and inroads the muscles strength levels more efficiently Less of the body's limited resources are wasted in the process of stimulating the muscles to grow leaving more for recovery and growth The ideal resistance curve for nearly all single joint exercises as well as compound pulling exercises such as the bent-over barbell row which require an exponential resistance decrease can only be provided by a properly designed machine In compound pushing movements however such as the squat and various presses the relatively flat resistance curve provided by the near vertical movement of a barbell will provide a relatively balanced variation in resistance Assuming that proper turnaround technique is used and lockout is avoided these will load the muscles relatively efficiently Figure B - Comparison of arm flexion strength curve with the resistance curve of a strict barbell curl Most compound pushing movements require a relatively flat resistance curve Most compound pulling and rotary movements require an exponential resistance decrease over the last half of the movement Direct Resistance In many barbell exercises the amount of resistance that can be used is limited by the strength of weaker intermediary structures preventing the targeted muscular structures from being loaded as meaningfully as possible In a properly designed machine the resistance can be applied directly to the target muscles without going through a weak link which allows them to be inroaded more efficiently A good example of this is the barbell squat Although the barbell squat is a highly productive exercise it is not as effective as a properly designed leg press for targeting the musculature of the hips and thighs since it requires those muscles to be loaded through the weaker musculature of the low back As a result the amount of weight one can handle in a barbell squat is limited by the strength of the lower back A properly designed leg press loads the muscles through the hips so the weight that can be used is only limited by the strength of the hip and thigh muscles While the barbell squat provides a greater amount of stimulation to the body as a whole due to the involvement of a larger amount of muscle a leg press machine will provide greater growth stimulation for the musculature of the hips and thighs The muscles of the chest back and shoulders can only be indirectly loaded through the weak links of the arm and grip muscles when using free weights Direct resistance for these muscle groups is only possible with machines Balance There is a common misconception that the need to balance a barbell dumbbells or the body during free weight exercises requires greater muscular effort and provides [http://www.rowlettmovers.com/ Rowlett Moving Company] more effective growth stimulation or growth stimulation to more of the body This is not true however since very little muscular effort is required to balance something

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