The Basics of Muscular Strength and Endurance:

Muscular strength and endurance are two health-related components of fitness that fall under the heading of resistance training type exercises, or exercises that improve muscular fitness. While this chapter will focus specifically on muscular endurance and muscular strength, there are also two other types of resistance training subgroups we can mention, which include training for muscular hypertrophy and training for muscular power. As defined in Chapter 3, Muscular Strength is the ability of skeletal muscles to overcome resistance, and Muscular Endurance is the ability of skeletal muscle to resist fatigue (ACSM, 2013). In Chapter 3, we also defined muscular power as it is a skill-related component of fitness. Muscular power is the ability to overcome a force at speed. Training for muscular power would certainly have benefits, specifically in sport (consider Olympic lifts). Muscular power, for the most part, is beyond the scope of this text. We can also mention training for muscular hypertrophy, which is training for the goal of increasing muscular size. While training for muscular endurance and/ or muscular strength will also lead to muscular hypertrophy, if someone’s primary goal is to increase muscular size (think bodybuilder or figure competitor) there would be some variations that will be mentioned below.

Types of Muscle Contractions

Muscle contractions can be dynamic or static (Kenny et al., 2015). Dynamic contractions cause joint movement. Dynamic contractions include concentric contraction and eccentric contractions. Concentric contractions are caused by muscle fiber (cell) shortening, while eccentric contractions are caused by muscle fiber lengthening. Many movements have a concentric and eccentric phase. Muscle contractions can also occur without movement at the joint, and muscle fiber length doesn’t change. These contractions are called static, or isometric contractions. For example, during a bicep curl, the raising of the weight is a concentric contraction, and the lowering of the weight is an eccentric contraction. A common core exercise that yields isometric contractions is a plank.

Why Participate in Resistance Training

There are many benefits of participation in resistance training that go beyond sport performance. For starters, having greater muscular strength and endurance makes performing everyday tasks easier (ACSM, 2013). These everyday tasks are often referred to as activities of daily living, or ADL’s. Besides making activities of daily living less stressful, the other main goal of a health related resistance training program is to prevent, manage, and/or slow the progression of various chronic diseases (ACSM, 2013). Three primary chronic conditions that resistance training can be particularly beneficial in doing this, include osteoporosis, obesity, and diabetes. As we age, we lose muscle mass and bone density. Age related loss in bone mass is referred to as osteopenia (Kenny et al., 2015), and a severe decrease in bone mass that leads to bone fragility and fractures is termed Osteoporosis.

Weight bearing exercise is important to maximize bone density early in life, and prevent its loss in middle aged and older adults.  It is particularly important that females participate in weight bearing activities as there is a much steeper decrease in bone mineral density in older women due to menopause in comparison to age matched males (Kenny et al., 2015). Resistance training is also important for managing body composition. Fat-free tissue is more metabolically active than fatty tissue (Kenny et al., 2015).  Thus, it is thought that if we can increase our muscle mass (part of our fat-free mass), we can increase our resting energy expenditure (also called resting metabolic rate). This would lead to our expending more energy at rest than prior to the increase in muscle mass.  We will dive deeper into the topic of body composition in Chapter 8.

Recommendations

The ACSM (2013) recommends participating in full-body resistance training at least 2 – 3 times a week (when there are no contraindications to resistance training). This would include resistance training for muscular strength or muscular endurance (or possibly muscular hypertrophy or power). Again, these are the minimum recommendations, and based on someone’s goals and interests completing resistance training more than 2-3 times per week may be ideal. While doing more can be great, it is also important to make time for muscle recovery. Doing so will help you reach your goals and also prevent injury. If you want to resistance train more often, the general rule is to avoid working the same muscle groups on back-to-back days, or giving 48 hours between working the same muscle group. Again, you can resistance train on back-to-back days, just make sure you work different muscle groups! If you are doing a full-body resistance training workout, you should give 48 hours rest between sessions.

Number and type of Exercises

The number of exercises you complete depends on your goals. Resistance training programs should first target multi-joint and compound movements (activating more than one muscle group) (ACSM 2013). Examples of these include chest presses, squats, back extensions, and crunches. While the first focus should be these multi-joint and compound movements, it is also alright to add single-joint movements such as the bicep curl and calf raises.

Sets And Repetitions

Ideally, each muscle group should be trained for 2-4 sets, which are bouts of exercise. Four sets per muscle group (whether it is the same movement or not) would be more beneficial than less. Still, once again, something is always better than nothing in the absence of contraindications, so even a single set is beneficial (ACSM 2013)!

Regardless of what your goals are, you will repeat each movement multiple times within each set. The number of complete movements within a set are repetitions. How many repetitions you complete will largely depend on your goals and how heavy the weight you are moving is (the resistance). For someone aiming to increase muscular strength, they would move relatively heavy weights with a low number of repetitions (1-5 repetitions). The weight would be somewhere between 60-80% of the individual’s one-repetition maximum or 1RM (more on 1RM under intensity) (ACSM, 2013). When lifting heavy weights, depending on experience, 1-3 min should be given between sets (Kenny et al., 2015).   For someone aiming to increase muscular endurance, they would move relatively lighter weight but for more repetitions (15-25 repetitions). The lighter weight would translate to a weight of roughly 50% of someone’s 1RM.  In addition, rest between sets should be less when training for muscular endurance (ACSM, 2013).

Intensity

When we talk about heavy vs moderate vs lightweight, or resistance, these are relative terms. For example, what is light for one person could be heavy for another! Also, what feels heavy to move one way might feel light to move another way. Typically, people can move more weight with their lower body vs. upper body. Often the resistance moved is expressed as a percentage of someone’s one repetition maximum (1RM) as mentioned above. A 1RM is a weight someone can correctly lift (specific to the movement) with one effort (Kenny et al., 2015). For example, if someone can bench press 100lb one time (and only one time), and they want to move 75% of their 1RM, they would bench press 75lb. To assess 1RM, an individual should warm up and select a weight they feel comfortable lifting at least one time. Weight is continuously added until the individual reaches a weight they can only move one time. An assessment of multiple RMs can also be used to assess strength (Reynolds et al., 2006). Some individuals should not perform an IRM test or a low RM test. According to the ACSM (2013), if an individual has metabolic disease, pulmonary disease, or is at risk for cardiovascular disease, a 15 RM would be a better option for assessing 1RM. Other conditions may also be contraindications to heavy lifting.

Assessing Muscular Fitness

Muscular Strength

As mentioned above, a 1RM  is the weight someone can correctly lift (specific to the movement) with one maximal effort (Kenny et al., 2015). A 1 RM test is a common way to measure muscular strength.  According to the ACSM (2013),  an assessment of multiple RMs can also be used to assess strengths. The chart linked below from the National Strength and Conditioning Association can be used to estimate 1RM based on a multiple RM test. For example, if someone can move 80 lb for 8 repetitions (and cannot complete more than 8 repetitions), their estimated 1RM is 100lb.

Training Load Chart

Muscular Endurance

Tests to assess muscular endurance are assessments that require repeated muscle contractions or holding a sustained muscle contraction. One example of a test for muscular endurance is the YMCA bench press test (ACSM, 2013). The YMCA bench press test requires individuals to complete as many correct repetitions as possible at the speed or rate of 30 repetitions per minute. The weight used for this assessment is 80 lb (36.3 kg) and 35 lb (15.9 kg) for males and females respectively. Other muscular fitness tests include the push-up and curl up test (ACSM 2013).  Both of these assessments require individuals to complete the maximal number of correct repetitions possible without a break, and without breaking correct form (or in the case of the curl up test the individual reaches 75).

You will be  completing these tests to assess your own muscular endurance. More information on the specifics of the push-up and curl up test can be found below under “Practical Applications/Laboratory Activities”