How should we train the triceps?
When training for bigger arms, it is important not to neglect the triceps. At three times the physiological cross-sectional area of the biceps, the triceps brachii are an essential component of the upper arm.
So how can we design a strength training program that will maximize the growth of the triceps? What factors do we need to take into consideration, and how do each of these factors affect the different variables within the training program?
What information do we need to identify the best approach to training a muscle group?
The basic functions of muscles can be identified from their anatomy. The most fundamental anatomical features of a muscle are its origin and insertion. These are the points that the muscle attaches to the skeleton. The origin is the point more proximal while the insertion is the point more distal. By locating the origins and insertions of a muscle, we can make basic predictions about its functions. In addition, when there are multiple muscles within a group, if they have slightly different origins and insertions, we can make predictions about how small differences in exercise performance might affect their relative contributions to a movement or exercise.
Many muscles have origins and insertions that mean that the muscle crosses only one joint while others have origins and insertions that mean that the muscle crosses two joints. Crossing one joint means that the muscle can only carry out one joint action while crossing two joints means that it can carry out two joint actions. When a muscle crosses two joints, it can display unpredictable behaviors if a movement or exercise involves moving both of these joints at the same time.
The triceps brachii muscle group is located on the rear side of the upper arm and lies adjacent to the humerus (the upper arm bone). It is made up of three heads: the medial head, the lateral head, and the long head.
The three heads of the triceps brachii have different origins. The origin of the medial head is on the medial, posterior side of the humerus while the origin of the lateral head is on the lateral, posterior side of the humerus (the origin of the medial head is also lower on the humerus than the origin of the lateral head). In contrast, as the only two-joint muscle of the group, the origin of the long head is on the infraglenoid tubercle of the scapula, which is at its most lateral point and on its inferior surface.
Each of the three heads of the triceps brachii insert on the olecranon process of the ulna (a forearm bone), ultimately reaching the same point, although the tendon of insertion of the medial head is deep to the other two heads. The insertions also differ insofar as the medial and lateral heads insert onto the medial and lateral sides of the olecranon, and insofar as the tendon of the lateral head continues onto the lateral and proximal aspect of the ulna.
Their very slight anatomical differences notwithstanding, all three heads of the triceps brachii can be expected to contribute to elbow extension, and the long head seems to contribute to shoulder extension as well.
Internal Moment Arm Lengths
Muscles exert turning forces on joints that are the product of their linear tension and their internal moment arm length. Therefore, longer internal moment arm lengths lead to greater turning forces. More importantly, when multiple muscles act on a joint, those with the longest internal moment arm lengths contribute to the greatest extent. Also, which muscles contribute most to the joint turning force alters according to the joint angle.
By studying the way in which the internal moment arm lengths of all the muscles acting on a joint change over the joint angular range of motion, we can identify the joint angle that involves the greatest contribution from each muscle. Having done this, we can then select exercises with strength curves that involve peak forces being required at the joint angles that involve the greatest contribution from the target muscle that we want to develop. This is particularly important when training muscles at joints controlled by multiple different muscles (such as the hip, which is extended by the gluteus maximus, hamstrings, and adductor magnus), but is also relevant when a muscle has multiple, independent heads, as is the case for the triceps brachii.
Triceps Internal Moment Arm Lengths
The triceps brachii comprises two single-joint heads (the medial and lateral heads) and one two-joint head (the long head). All three heads contribute to elbow extension moments while the long head also contributes to shoulder extension. The contributions of each head are affected by both elbow and shoulder angles.
- Elbow Extension
The elbow extension internal moment arm lengths vary between the heads of the triceps brachii and also vary over the joint range of motion in different ways. Overall, the elbow extension internal moment arm length of all three heads gradually decreases from its peak when the elbow is flexed (bent) to its smallest length when the elbow is extended (straight). More importantly, the triceps brachii long head contributes most to elbow extension when the elbow is extended, while the medial and lateral heads contribute to a greater extent when the elbow is flexed. This indicates that we can preferentially train the long head with exercises that involve exerting peak force with a straight arm (elbow extension) and the medial and lateral heads with exercises that involve producing peak force with a bent arm (elbow flexion).
Additionally, the contributions of each head to elbow extension are affected by shoulder angle. At low shoulder angles (arms by the sides), the long head is the main contributor to elbow extension, regardless of elbow angle. As shoulder angle is increased, the medial and lateral heads become more important. Practically speaking, this suggests that the long head can be best trained with exercises that involve peak force being exerted with the arms by the sides (shoulder extension). In contrast, the medial and lateral heads can be best trained with exercises that involve peak force being exerted with the arms elevated (shoulder flexion).
- Shoulder Extension
Few studies have assessed the role of the triceps brachii long head as a shoulder extensor, most likely because other muscles are considered to be the prime movers in this regard.
One study recorded the involuntary shoulder extension turning force produced by electrical stimulation of the triceps brachii long head. After subtracting the passive moment caused by the position of the shoulder, the turning force for shoulder extension increased from 0–120 degrees of shoulder elevation in the scapular plane (0 degrees is the anatomical position with the arms resting by the side), likely as a result of an increasing internal moment arm length. Yet, the turning force produced at all joint angles was small, which might be due to the involuntary nature of the contraction, or it may reflect the relatively small involvement of this muscle in shoulder extension compared with prime movers such as the latissimus dorsi and pectoralis major. Yet, other research shows that the muscle is moderately active in exercises such as the free weight pullover.
- Working Sarcomere Lengths
Muscles grow after their fibers are exposed to a high level of mechanical tension. The amount of tension that muscle fibers experience can be increased by stretching their passive structures (mainly titin). Consequently, using a full range of motion for a strength training exercise can increase hypertrophy but only if this leads to titin being stretched.
However, the titin molecules inside muscle fibers are only stretched when the sarcomeres of the muscle fibers in a muscle are lengthened as far as the descending limb. Lengthening a muscle to a stretched position using a full range of motion does not always cause the sarcomeres of its muscle fibers to reach this point. Some muscles contain muscle fibers that have sarcomeres that operate entirely on either the ascending limb or the plateau region of the length-tension relationship. As a result, they do not experience any increase in passive tension when the muscle itself is stretched.
Therefore, to identify the best range of motion for a muscle, we need to look at the range of working sarcomere lengths for that muscle to see whether they can reach the descending limb. When muscles contain muscle fibers with sarcomeres that reach the descending limb, we may decide to use full ranges of motion in most exercises since this should stimulate stretch-mediated hypertrophy. In contrast, when muscles contain muscle fibers with sarcomeres that remain mainly on the ascending limb or plateau regions, we may decide to use some exercises with partial ranges of motion, either for variety or to reduce the amount of muscle damage that is caused.
Working Triceps Sarcomere Lengths
When muscles produce force, the amount of force they produce is primarily determined by the force-velocity and length-tension relationships of the working muscle fibers.
If different muscles within a group (or different regions within a muscle) are contracting at different velocities or from different starting lengths, then they will produce different amounts of force and, therefore, also experience different amounts of mechanical loading. Moreover, when a muscle works predominantly on the descending limb of the length-tension relationship, it is more likely to experience an additive effect of passive and active tension during strength training with a large range of motion because of greater stretch-mediated signaling.
The working sarcomere lengths of the triceps brachii do not seem to reach far beyond the plateau region of the length-tension relationship. When measured from 30–120 degrees of elbow flexion (0 degrees = full elbow extension), the lateral head of the triceps brachii remains largely on the plateau while the long head works on the plateau and on the early part of the descending limb. This suggests that only the long head of the triceps is likely to experience any stretch-mediated hypertrophy, and then only when working at its end range of motion. However, the internal moment arm lengths mean that the long head is least active when it is working in this range of motion.
This is probably why most studies that have compared the effects of strength training with full and partial ranges of motion in the triceps brachii have reported no beneficial effects of the full range of motion, despite most studies in the quadriceps finding a beneficial effect. In practice, this means we can freely make good use of partial range of motion exercise variations when training the triceps brachii as it will likely respond similarly regardless of the range of motion used (or longest muscle length achieved) in training.
- Susceptibility to Muscle Damage
Susceptibility to muscle damage after a workout helps us to identify the right training volume, loading types, and frequency since these factors are largely a function of how easy it is to damage a muscle during any given workout.
Susceptibility to muscle damage after a workout can be directly assessed by recording strength recovery. Where this information is not available, it can be inferred based on several factors. Factors that affect the susceptibility of a muscle to muscle damage after a workout include (1) the prevailing fiber type of the muscle, (2) the level of voluntary activation that can be attained by the muscle, (3) the size of the muscle, and (4) the working sarcomere lengths of the muscle fibers inside the muscle.
- Prevailing Fiber Type of the Muscle — The prevailing fiber type of the muscle affects the amount of muscle damage that occurs after a strength training workout because fast twitch muscle fibers are more easily damaged than slow twitch muscle fibers (perhaps due to their less oxidative capacity or to the stiffer titin molecules that they contain). Therefore, muscles that contain a proportion of fast twitch muscle fibers will experience greater damage after a workout.
- Level of Voluntary Activation — The level of voluntary activation that can be attained by the muscle during a muscular contraction affects the amount of muscle damage that occurs after a strength training workout since higher levels of motor unit recruitment allow the activation of more fast twitch muscle fibers, which are more easily damaged. Therefore, muscles that can achieve greater voluntary activation will experience greater damage after a workout.
- Size of a Muscle — The size of a muscle affects the amount of muscle damage that occurs after a strength training workout because larger muscles tend to achieve lower levels of voluntary activation during maximal contractions and display greater central nervous system fatigue during fatiguing exercise. Both lower levels of voluntary activation and greater central nervous system fatigue are protective against muscle damage occurring. Therefore, it can be expected that smaller muscles will experience greater muscle damage than larger ones.
- Working Sarcomere Lengths — The working sarcomere lengths of the muscle fibers within a muscle affect the amount of muscle damage that occurs after a strength training workout because longer sarcomere lengths lead to greater passive tension and, therefore, produce greater damage to the internal structures within each muscle fiber.
Triceps Susceptibility to Muscle Damage
Research that has studied the effects of a standard workout on a number of muscle groups has found that the triceps takes longer to recover from a standardized workout than many other muscles.
This might be expected given that the triceps brachii is more fast twitch than many other muscles (and the long head may be more fast twitch than the lateral and medial heads). Also, the triceps brachii reaches high (94–96%) levels of voluntary activation during maximal isometric contractions. This is noteworthy given that the muscle is actually quite large in comparison with many other muscles in the upper body. Even so, the triceps brachii may not be as easily damaged as some other muscles because it operates mostly on the plateau region of the length-tension relationship.
In practice, this means that we should avoid training the triceps brachii (especially the long head) in ways that increase muscle damage, such as by using high repetition sets, high volumes, and larger ranges of motion. Also, accommodating resistance in the form of elastic resistance may be a better option than conventional free weights. Additionally, despite using these methods, we may still need to train the muscle less frequently.
- Regional Muscle Variation
Although we often think about muscles as being single entities, they are actually made up of multiple functional units, which are sometimes called muscles within muscles. These functional units contribute differently to force production depending on (1) the direction of movement at the joint and (2) the point in the joint range of motion at which force is greatest.
Regional variation can be identified by anatomical study (to identify the presence of any subdivisions inside the muscle, such as may be caused by intramuscular tendons), by analysis of the innervation of the muscle (to assess whether there are multiple nerves leading to different parts), and by assessment of regional muscle activation during a range of different exercises (to see which regions are most active). Where such regions exist, multiple exercises may be necessary to achieve maximal hypertrophy because different exercises will involve the preferential recruitment of motor units within the different regions.
There is evidence that each of the three heads of the triceps (and perhaps also two regions within the medial head) receive separate motor innervation. However, the exact nature (and the functional importance) of this regional innervation is still unclear. Therefore, it is unknown whether we need to use multiple exercises to train different parts of each of the muscles.
It is generally assumed that the three triceps brachii heads are mainly innervated by the radial nerve, which splits into four branches to innervate (1) the long head, (2) the distal medial head, (3) the lateral head, and (4) the proximal medial head. The radial nerve is one terminal branch of the posterior cord of the brachial plexus while the axillary nerve is another. However, some research has found that the long head of the triceps brachii may actually be innervated by the axillary nerve. Even so, it seems likely that while this may be the case for some individuals, it is not true for everyone. Also, it is possible that at least one region of the medial head may be innervated by the ulnar nerve, which is itself a continuation of the medial cord of the brachial plexus. However, this remains controversial.
What is the takeaway?
The triceps brachii comprises three separate heads, which can be trained with different exercises. The long head can be best trained with exercises that involve peak contractions with a straight arm (elbow extension) while the arms are by the sides (shoulder extension). The medial and lateral heads can be best trained with exercises that involve peak contractions with a bent arm (elbow flexion) while the arms are elevated (shoulder flexion). While some research indicates that there is regional variation within the medial head of the triceps brachii, it is unclear how each region might be targeted.
The triceps brachii is a large, very fast twitch muscle group for which we can achieve very high levels of voluntary activation. Even though it works mainly on the plateau of the length-tension relationship, it is therefore easily damaged by training. This indicates that we will want to prioritize training approaches that reduce muscle damage (such as exercises with descending strength curves, partial ranges of motion, or accommodating resistance). We may also want to reduce volume (if we keep training frequency the same as other muscle groups) or train the muscle less frequently (if we keep training volume the same as other muscle groups).
Since the triceps brachii works mainly on the plateau of the length-tension relationship, attempting to achieve stretch-mediated hypertrophy by selecting mainly full range of motion exercises is unlikely to be more effective than partial range of motion equivalents. Given that full ranges of motion cause more muscle damage, and it is important to avoid muscle damage for this muscle group, partial range of motion variations may be the best option.
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