Which Of The Following Is Equipment With A Constant Resistance - T-Tees - Your Answers Await, Life's Questions Unraveled

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This is an excerpt from NSCA’s Essentials of Personal Training 3rd Edition With HKPropel Access by NSCA -National Strength & Conditioning Association,Brad Schoenfeld & Ronald L. Snarr.

By Ronald L. Snarr, PhD, and Alexis Batrakoulis, PhD

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Common Types of Resistance Training Equipment

Although many variables must be taken into consideration when designing a resistance training program, choosing the proper equipment or machine is essential. The choice of modality should be based on several factors, including the client’s training status (i.e., beginner, intermediate, or advanced), proficiency of the movement, anthropometrics (e.g., height, weight), and personal preference.

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Resistance training equipment falls into three main categories:

Constant resistance throughout a range of motion (ROM)
Variable resistance throughout a ROM
Constant speed of contraction during a given ROM

Each piece of equipment provides unique advantages; thus, common types of weight training machines, free weights, and alternative equipment will be described in this chapter.

Machines

Weight machines allow the individual to perform single or multijoint movements in a restricted and controlled plane of motion without a spotter, while increasing ease of use and stability for the client. Machines are particularly useful for special populations (e.g., elderly), inexperienced clients, and those recovering from injury. However, all individuals, regardless of training status, can benefit from the addition of machine-based exercises within their resistance training regimen. Machines can also be adjusted to accommodate most individuals of varying heights and segment lengths; however, they may not be ideal for smaller or larger individuals depending on the machine’s biomechanical design. Although machines have multiple advantages, they can be costly and can require large amounts of space; further, several units are often needed to target all the major muscle groups. This may particularly affect those who train in group settings, in one-on-one studios, or at home. Thus, personal trainers may opt for free weights or alternative resistance training equipment for a particular exercise if a machine is not feasible. The features of the most common types of resistance training machines are described next.

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SelectorizedSelectorized machines use a series of cables and pulleys to lift a built-in vertical weight stack. These machines provide constant resistance and a preset movement pattern that theoretically helps reduce the risk of injury while ensuring proper exercise technique. Additionally, selectorized machines provide the client an easier and quicker way to change the weight selection as opposed to plate-loaded machines and free weights.

Plate LoadedAs compared with selectorized, plate-loaded machines require the use of external resistance via conventional free-weight plates. Since this involves manually loading the device with resistance, plate-loaded machines increase risk of injury to clients when loading and unloading weight. Plate-loaded machines are often capable of supporting more weight and offer a smoother movement pattern versus selectorized because of the diminished frictional resistance.

CamCam-based machines offer a form of variable resistance that increases or decreases load assistance based on the strength curve; however, absolute load does not change throughout the ROM. These machines are based on joint kinetics and forces associated with the particular joint or joints used within the movement. For example, at the start of a chest press with the handles close to the body, a greater force production is required to push through the sticking point (the most difficult part of the exercise) as compared with the remainder of the movement. Thus, the cam allows for a greater load assistance earlier in the concentric phase and less assistance past the sticking point.

Rod or Linear GuidedRod machines provide constant resistance during a given exercise and are usually plate loaded. These machines allow movement in a straight (linear) path only, thereby increasing stability. Additionally, most rod machines contain safety mechanisms that allow the use of heavier weights without a spotter; however, if applicable, a spotter is always recommended. The most common types of rod machines are the Smith machine, leg press, and hack squat.

HydraulicHydraulic machines incorporate fluid-filled (oil or water) pistons and cylinders to achieve resistance as a client works through a given ROM. A major advantage of hydraulic machines is there are no external plates or weight stacks that may potentially cause an injury if a client loses his or her grip or is unable to complete the full ROM because of muscular failure. Additionally, the hydraulic resistance can be increased by either reducing the length of the lever or performing the movement quicker through a given ROM. Because pistons are used, the client can perform only the concentric portions of an exercise. For example, after performing a chest press-style movement by pushing the levers away from the body, the client must pull the handles back to the starting position. Thus, personal trainers must consider the implications of using concentric-only movements.

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Air or PneumaticAir or pneumatic machines use compressed air cylinders rather than selectable weights or external plates to add resistance. Pneumatic machines allow individuals to perform high-velocity movements with a reduced risk of injury as compared with traditional resistance machines. Depending on the design of the machine, exercises can be performed in either one plane of motion or within a three-dimensional space. Each repetition is fully controlled via pressurized air, and resistance can be easily adjusted as needed. However, one of the major drawbacks is the need for an air compressor with each unit to supply the resistance. Additionally, pneumatic machines are costly, require different units to target all the major muscle groups, and require a large amount of space.

IsokineticIsokinetic machines, or accommodating variable-resistance machines, allow for the speed of contraction to be held constant throughout a given ROM. As an exercise is performed, the muscular effort from the client is matched with a proportional amount of resistance that maintains contraction speed. Unlike other resistance training machines, isokinetic machines are computer controlled and can be programmed to function through a specific ROM or provide concentric- or eccentric-only resistance. Because of their high cost and required knowledge of complex computer programming, isokinetic machines are typically found only in clinical, rehabilitation, and laboratory settings. Furthermore, they do not allow for exercises to be performed in multiple planes of motion or for certain multijoint movements (e.g., squat, bench press).

Free Weights

Unlike machine equipment, free-weight equipment such as barbells, dumbbells, and kettlebells allow unrestricted movement in all planes of motion, rather than a largely fixed movement path.

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BarbellsOne of the most common forms of free weights are barbells, which allow the client to perform multi- and single-joint movements in all planes of motion. Barbells are available in a variety of shapes, weights, and lengths. Thus, certain exercises may warrant proper fitting of the barbell to the client and exercise. For example, the bench press exercise is commonly performed with a longer straight bar, while the biceps curl often uses a shorter, bent EZ-curl bar to allow for a more natural position of the elbow and wrists.

A standard barbell is about 1 inch (2.5 cm) in diameter and weighs approximately 5 pounds per foot (about 7.5 kg per meter). Some standard barbells (there are also EZ-curl bar varieties) are fixed at a preset weight that cannot be adjusted but are typically available in 5- to 10-pound (2.5-5 kg) increments. An Olympic barbell is about 7 feet (2 m) long and weighs 45 pounds (20 kg), with the section where the weight plates are placed having a diameter of approximately 2 inches (5 cm).

Since barbells are free moving, the personal trainer should assess clients to determine if they possess the required coordination, stability, and increased knowledge of proper technique to safely perform a movement.

DumbbellsDumbbells allow for multi- and single-joint resistance training exercises to be performed within all planes of motion. Dumbbells vary in size and shape, ranging from 1 pound (0.5 kg) to over 100 pounds (45 kg), and are typically made from cast iron or rubber (with a steel handle). Equipment advantages include minimal space requirements, easily transportable, and the possibility of decreasing muscular imbalances through unilateral exercises. Although benefits include increased muscular strength and joint stability, an initial level of joint stability is required before a client can use free weights. Personal trainers should take this into account when working with specific populations.

KettlebellsAn alternative to dumbbells, kettlebells are a highly versatile modality and allow for a variety of exercises with minimal space and equipment. Where dumbbells have an equal weight distribution, kettlebells have an offset center of mass that allows for more momentum-based movements (e.g., swings). Kettlebells are typically made with cast iron, rubber, or hard plastics and have various sizes of hand grips (e.g., cast iron kettlebell handles increase in thickness as the weight increases), which may be a consideration for personal trainers working with special populations.

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