19 Muscular Strength and Endurance

Muscular Physiology

There are over 600 muscles in the human body; they are responsible for every movement we make, from pumping blood through the heart and moving food through the digestive system, to blinking and chewing. Without muscle cells, we would be unable to stand, walk, talk, or perform everyday tasks.

There are three types of muscle:

  1. Skeletal: responsible for body movement
  2. Cardiac: responsible for the contraction of the heart
  3. Smooth: responsible for many tasks, including movement of food along intestines, enlargement and contraction of blood vessels, size of pupils, and many other contractions

Skeletal Muscle Structure and Function

Skeletal muscles are attached to the skeleton and are responsible for the movement of our limbs, torso, and head. They are under conscious control, which means that we can consciously choose to contract a muscle and can regulate how strong the contraction actually is. Skeletal muscles are made up of a number of muscle fibers. Each muscle fiber is an individual muscle cell and may be anywhere from 1 mm to 4 cm in length.

When we choose to contract a muscle fiber – for instance we contract our bicep to bend our arm upwards for a biceps curl – a signal is sent from our brain via the spinal cord to the muscle. This signals the muscle fibers to contract. Each nerve will control a certain number of muscle fibers. The nerve and the fibers it controls are called a motor unit. Only a small number of muscle fibers will contract to bend one of our limbs, but if we wish to lift a heavy weight then many more muscles fibers will be recruited to perform the action. This is called muscle fiber recruitment.

Muscular strength is the amount of force that a muscle can produce one time at a maximal effort, and muscular endurance is the ability to repeat a movement over an extended period of time. Resistance training is the method of developing muscular strength and muscular endurance, which in turns improves wellness.

Role of Muscles

When one muscle contracts and shortens, another opposing muscle will relax and lengthen. In this way, muscles are arranged in pairs. An example is when you bend your arm at the elbow for a biceps curl: you contract and shorten your biceps muscle and relax and lengthen your triceps muscle. This is the same for every movement in the body. There will always be one contracting muscle and one relaxing muscle. If you take a moment to think about these simple movements, it will soon become obvious that unless the opposing muscle is relaxed, it will have a negative effect on the force generated by the contracting muscle.

A muscle that contracts, and is the main muscle group responsible for the movement, is called the agonist or prime mover. The muscle that relaxes is called the antagonist. Although the agonist/antagonist relationship changes depending on the exercise, every muscle group has an opposing muscle group.

Below are examples of agonist and antagonist muscle group pairings:

Agonist (Prime Mover) Antagonist
(mid/upper back)
Rectus Abdominus
Erector Spinae
(back muscles)
(front of thigh)
(back of thigh)
Tibialis Anterior
(front of lower leg)

Smaller muscles may also assist the agonist during a particular movement. The smaller muscle is called the synergist. An example of a synergist would be the deltoid (shoulder) during a push-up. The front of the deltoid provides additional force during the push-up; however, most of the force is applied by the pectoralis major (chest).

Other muscle groups may also assist the movement by helping to maintain a fixed posture and prevent unwanted movement. These muscle groups are called stabilizers. An example of a stabilizer is the shoulder muscle during a biceps curl or triceps extension.

Types of Muscular Contraction

Isometric: This is a static muscle contraction where the length of the muscle does not change. The force exerted is equal to the resistance and movement at the joint stops. Examples include a plank or wall-sit.

Isotonic: This is a moving contraction, also known as dynamic contraction. During this contraction there is movement at the joint. There are two types of isotonic contractions:

  • Concentric: This is when the muscle contracts and shortens against a resistance. This may be referred to as the lifting or positive phase. For example, during a biceps curl when the bar is curled from the straight arm position to the fully flexed position, the biceps are going through a concentric contraction.
  • Eccentric: This occurs when the muscle is still contracting and lengthening at the same time. This may be referred to as the lowering or negative phase. For example, during the biceps curl exercise as the bar is lowered at a slow, controlled speed from the fully flexed position to the fully extended position, the biceps are going through an eccentric contraction.

Major Muscles

Major Muscles of the Arm

  • Deltoids
  • Biceps
  • Triceps

Major Muscles of the Leg

  • Glutes
  • Quadriceps
  • Hamstrings
  • Adductors
  • Calves

Major Muscles of the Front Torso

  • Pectorals
  • Abdominals
  • Obliques

Major Muscles of the Back Torso

  • Latissimus dorsi
  • Trapezius
  • Rhomboids
  • Erector Spinae

Muscular Strength and Endurance Training Prescription

An effective resistance training program should be progressive and repeat itself periodically. This can be accomplished by increasing the resistance in a systematic manner and repeating the exercises on a regular basis (e.g., Monday, Wednesday, and Friday). Variability can be included in a resistance training program by changing exercises on a regular basis. There are multiple different exercises for each of the major muscle groups making program variability a viable and productive option. A resistance training log can be used to help keep track of program changes in exercises, intensity, and frequency. The chart below outlines recommendations for frequency, intensity, time, and type of resistance training for beginners as well as those more experienced.

Additional guidelines include:

  • Perform a minimum of 8 to 10 exercises that train all of the major muscle groups
  • Prioritize compound, or multi-joint exercises, which involve more muscles with fewer exercises
  • Perform exercises through a full range of motion, in a controlled manner and with a normal breathing pattern
  • Exercise sequence should follow large before small muscle group exercises, multi-joint exercises before single-joint exercises, and higher intensity before lower intensity exercises


Resistance Training Systems

When creating a resistance training program, there are several training systems that can be used. Each has different benefits associated with them.

Circuit Training

In circuit training the individual will perform a series of exercises in sequence with minimal rest between exercises. Typically, in circuit training you will have all major muscle groups addressed within the variety of exercises within the circuit and will only perform a single set of each exercise. This type of training is time efficient and effective for developing muscular endurance and general conditioning.


Super set training involves performing two exercises targeting opposing muscle groups (e.g., front and back of the body or upper and lower body) in rapid succession from one another with minimal or no rest between the exercises. Examples include biceps curl and triceps kickback (front and back of body) and overhead press and squats (upper and lower body). Super-setting is beneficial to optimize time-management during resistance training and to increase cardiovascular load through minimal rest breaks. This training technique also helps to correct muscle imbalances in the body.

Giant Set

Training with giant sets involves performing muscle exercises for a single muscle groups in rapid succession from one another with minimal or no rest between the exercises. For example, a giant set for the triceps could be triceps pushups, triceps overhead extension, and triceps kickbacks. Giant sets are time effective, improve muscular and cardiovascular endurance, and provide the opportunity to target all muscle fibers for a specific muscle.

Eccentric Training

In eccentric training (also known as negative training) there is focus on the eccentric phase of the movement. An exercise is performed with a normal concentric speed and then lowered slowly (5-7 seconds) during the eccentric phase. The increased emphasis on the lengthening phase supported increased strength grains and allows you to become more proficient in that movement. With eccentric training you can often enlist heavier weights than you might otherwise be able to lift. Once the fibers that were activated during your eccentric training become stronger, you will then be able to handle heavier weight concentrically as well.

Ladder and Pyramid Training

In ladder training a single exercise is performed for 3 or more sets with and increasing (ascending ladder) or decreasing (descending ladder) of resistance and/or reps with each set. Pyramid training involves using both ascending and descending ladders together. If changing resistance and reps with each set, they  should follow an inverse relationship meaning that as you increase the repetitions the weight decreases while if you decreased the number of repetitions the weight increases. With this type of training workouts are time efficient, short, and intense. They are effective, especially if you hit a plateau as you obtain greater volume with less rest. This is a good workout for variety as it can be done with any type of training equipment or body weight and is a great partner workout (e.g., “I go, you go”).

Drop Set

Drop sets is a system of training that involves completing a set of an exercise to fatigue, decreasing the weight 10-15%, and again performing as many repetitions as possible to fatigue. This is repeated for a total of 3-5 sets. Drop sets can be performed as a standalone training strategy or incorporated into other systems (such as super sets) where your final set is a drop set performed to failure. This is an advance training technique that can help to overcome performance plateaus as you accumulate volume in a shorter amount of time. It is also time effective without hindering muscle growth and will elicit more metabolic stress than you would with standard straight sets.



Libretexts. (2021, June 16). 4.2: Resistance exercise programing. Medicine LibreTexts. https://med.libretexts.org/Bookshelves/Health_and_Fitness/Concepts_of_Fitness_and_Wellness_(Flynn_et_al.)/04%3A_Muscular_Strength_and_Endurance/4.02%3A_Resistance_Exercise_Programing

Dawn Markell & Diane Peterson, Health and Fitness for Life. MHCC Library Press. Sept 4, 2019. https://mhcc.pressbooks.pub/hpe295

North Carolina State University Department of Health and Exercise Studies. Health and Exercise Wellbeing (8th.ed.). Plymouth, MI: Hayden McNeil.


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