TRAINING ARTICLES

Shaping a Muscle: Myth or Fact?

“You can’t target one part of a muscle. All over the web you’ll find bodybuilding articles about shaping your muscles. In these articles, authors claim that you can modify the shape of your muscles by training them in various, unconventional ways. A case in point is the all-too-common apocryphal advice about “peaking your biceps.” The writers of articles such as those will have you performing all sorts of bicep peak exercises that are purported to change the shape of the muscle. The truth is: you can’t change a muscle’s shape, only its overall size. The muscle origin and insertion is fixed, you won’t alter it with training other than to strengthen your tendons (or damage them with ultra-intense isolation movements).”1

The above quote sums up why we have decided to write this article. The concept of shaping a muscle is controversial, but going beyond opinions (as above) and adding some science and practical recommendations to the picture will shed new light on the issue of shaping a muscle.

Let’s begin by clarifying a couple of things about shaping a muscle:

  • Tendon cannot become muscle.
  • A distinction should be made between trying to shape one muscle and trying to change the shape of a body part.

The concept of shaping a muscle has the fancy name of “regional muscle hypertrophy” in scientific literature, and an extensive review gives many great points on the topic:2

  • A muscle can be divided into neuromuscular compartments, which are distinct regions of the muscle, each of which is innervated (activated) by an individual nerve branch and therefore contains motor unit territories with a unique set of characteristics. In other words, different portions of a muscle may be called into play depending on the task and demands of the situation. It is because each compartment has its own innervations that one can selectively recruit a particular region of that muscle.

    Functional differentiation within skeletal muscle refers to the ability of the central nervous system (CNS) to control, with a degree of independence, individual subunits of a muscle during a particular muscle contraction. Essentially, the concept of functional differentiation within skeletal muscle suggests an ability of the CNS to selectively activate those segments of a muscle which have the most appropriate line of action for the task as a means of ensuring the muscle’s efficient utilization.4

  • The concept of task specificity may help explain the regional hypertrophy.5 Several studies show non-uniform (regional) hypertrophy within a muscle: Knee extensions cause a 19% increase proximally (close to the hip), but only 13% increase in the central portion of the muscle. Elbow extensions have the greatest changes proximally and at middle levels, but less hypertrophy distally. While there is solid evidence of preferential activation of certain parts of a muscle, it is not yet proven that this preferential activation will result in regional hypertrophy.2
  • Some muscles (for example, the latissimus dorsi) have a greater portion of slow-twitch fibres in the deep region of the muscle and a greater portion of fast-twitch fibres in the outer layers of the muscle. In the semitendinosus (medial hamstrings), there are more fast-twitch fibres distally than proximally. Because fast-twitch fibres (type II fibres) grow more as a result of heavy resistance training than slow-twitch fibres, it can be speculated that there could be selective growth in that area.2

Both intra- and intermuscular activation patterns can change with very slight alterations in movement pattern, eccentric versus concentric actions or changes in velocity.5 The following section reviews a number of studies relating to specific body parts.

Calves

A study examined barbell calf raises (with a total load of 135% body weight) standing on a 3.81 cm block and performed in a 1-0-1 tempo. The subjects performed the calf raises without shoes, in three different conditions: (1) hips/knees/feet in neutral (pointing straight ahead), (2) hips/knees/feet maximally internally rotated (feet pointing inward) and (3) hips/knees/feet maximally externally rotated (feet pointing outward). The knees were kept straight in all conditions. During the internally rotated position, there was a significant greater muscle activation in the lateral gastrocnemius head compared to the medial gastrocnemius head. During the externally rotated position, there was a significantly greater muscle activation in the medial gastrocnemius head compared to the lateral gastrocnemius head. The authors speculate that the different positions affect the line of action, angle of pennation (angle between muscle fibre and tendon) and muscle fibre length of the two heads of the gastrocnemius, all affecting the muscles’ ability to produce force. The results might be specific to the barbell calf raise, the amount of load used, the degree of external rotation and the unshod (no shoes) condition.

Another study compared muscle activation between calf raises with various knee angles (90, 135 and 180 degrees). The soleus muscle (the deep part of the calf) showed significantly greater activation during plantar flexion at the 90 degree angle. The medial gastrocnemius showed significantly greater activation at a 180 degree angle. There was less difference in the lateral gastrocnemius when knee angles were compared.

Practical application

  • Perform calf raises with knees straight and internally rotated hips (point the feet inwards) to target the lateral gastronemius. Perform calf raises with knees straight and externally rotated hips (point the feet outwards) to target the medial gastrocnemius.
  • Perform calf raises with the knees bent to target the soleus muscle.
  • While the gastrocnemius shows an approximate equal distribution of slow-twitch and fast-twitch fibres, the soleus muscle is slow-twitch dominant (70 to 80%). Therefore, the soleus may respond better to higher reps, while the gastrocnemius may respond better to lower reps.

Hamstrings

According to Dr. Ken Kinakin, author of Optimal Muscle Training, we can emphasize the lateral hamstrings (the biceps femoris muscle) by performing hamstring curls with the hips in an externally rotated position and the feet pointing outward. We can emphasize the medial hamstrings (semitendinosus and semimembranosus) by performing hamstring curls with the hips in internal rotation and the feet pointing inward. With the hips in neutral and the feet pointing straight ahead, both heads are emphasized equally.10

A recent study compared various hamstrings-oriented exercises: kettlebell swings and Romanian deadlifts targeted specifically the semitendinosus over the biceps femoris. In contrast, supine leg curls and hip extensions specifically targeted the biceps femoris over the semitendinosus.11

Practical application

  • Regardless of the type of hamstring curl you perform, make sure to perform sets with the hips in external rotation as well as sets with the hips in the internally rotated position.
  • Make sure to engage the hamstrings in both exercises that focus on hip extension and exercises that focus on knee flexion.

Quadriceps

The prefix “quadri” means “four” and refers here to the four muscles that compose the front of the thigh: the rectus femoris, the vastus lateralis, the vastus intermedius and the vastus medialis obliqus (VMO) – the teardrop muscle. Often, it is this “teardrop” that seems to be the most difficult part of the quads to develop. Interestingly, it is also a key target for therapists during treatment of so-called patella-femoral pain syndrome, which is often associated with a ratio of vastus medialis to vastus lateralis of about 0.54:1. This means that the vastus lateralis is pulling on the patella (the kneecap) almost twice as hard as the vastus medialis muscle.18

extensions showed a preferential activation of the vastus lateralis (typically not a good thing!).18 If you perform the open-chain knee extensions, it might be important to medially (internally rotate the tibia) and restrict the range of motion to “terminal knee extension” (the last 15 degrees) as this way of performing knee extensions results in the highest level of activity of the VMO.19 If you really want to “kill it,” squeeze a medicine ball between your ankles as you perform this exercise.

Practical application

  • Maintain full-range-of-motion Olympic-style barbell squats as your primary exercise for the quads.
  • Finish with a loaded wall sit, where you hold plates, dumbbells or a bar while squeezing a medicine ball between the legs.
  • Perform knee extensions only in the top 15 degrees and with the hips in internal rotation (possibly with a medicine ball squeezed between the legs).

Abdominals

The key question often posed is if we can train the upper and the lower abdominal muscles separately or if it is all just one muscle.

“Upper abdominals” are defined as the muscle actions required to “flex” the upper trunk (while holding the pelvis stationary), and “lower” abdominals are defined as the muscle actions that are involved in holding the pelvis in posterior tilt (with the upper body held stationary).21 Thus, the definition above is based on the muscle action: The upper abdominals are the part of the abdominal musculature that move the trunk towards the pelvis with the pelvis held stationary, and the lower abdominals are the part of the abdominal musculature that move the pelvis towards the rib cage with the rib cage held stationary. When the movement pattern changes from pelvis to thorax motion, different neuromuscular compartments (in the total abdominal musculature) come into play.22 (Read: Different parts of the abdominal musculature are recruited.) In some cases, these differences may be too small to be of importance for training, and the ability to selectively recruit individual portions of the abdominal muscles may be based on the individual’s ability to perform the exercise correctly.23,24,25

Many research studies refer to the upper rectus abdominis (above the bellybutton) as the “upper abdominals” and the lower rectus abdominis (below the bellybutton) as the lower abdominals. This is a distinction based on anatomy rather than muscle function (as above).

Practical application

  • Pelvis movements result in higher activation in the obliques.22,23
  • Crossed-leg curl-ups target the lower rectus abdominis muscles.23
  • Preferential activation of the upper rectus abdominis takes place during a curl-up. Preferential activation of the lower rectus abdominis takes place during a posterior tilt exercise.25
  • Differences in activation of the upper and lower rectus abdominis in a curl-up versus bent leg raise may not become significant until fatigue is reached.26
  • During a stability ball curl-up and stability ball roll-out, the activity of the upper rectus abdominis is significantly greater than the activity of the lower rectus abdominis.27
  • During the stability ball jackknife exercise, the activity of the lower rectus abdominis is significantly greater than the activity of the upper rectus abdominis.27

Chest

Fifteen college-aged men with at least one year of weight-training experience and the ability to bench press their body weight at least one time were tested for their 1RM in an incline bench press (bench set at +30 degrees) and decline bench press (bench set at -15 degrees). The subjects’ 1RM in the decline press was 14.5% higher than in the incline press.

On a separate day, the participants performed 1 set of 6 repetitions with 70% of the 1RM in each condition. The lifting tempo was set at 1.5 seconds up and 1.5 seconds down. Recordings of muscle activation levels showed significantly increased activation of the sternal portion of the pectorals major (“lower chest”) in the decline bench press compared to the incline bench press. There was no difference in muscle activation levels for the clavicular portion of the pectorals major (“upper chest”) for the two conditions. The authors emphasize that the difference seen might be less during a set to failure.12

In another study, 15 male subjects with at least one year of resistance training experience and the ability to bench press at least 100% of their body weight were tested for their 1RM with the bench set at four different angles: flat, +28, +44 and +56. The subjects chose their own hand spacing, but the same hand spacing was used for all four conditions. The repetition maximum load decreased with the increasing angle of the bench.

On a separate day, muscle activity was recorded during 1 set of 5 repetitions with 70% of the 1RM in each condition. The tempo was 1.5 seconds up and 1.5 seconds down. Muscle activity was recorded during the lifting phase only. The results indicated a significant increase in the clavicular head of the pectorals major with the bench set at 44 and 56, but not 28 degrees. The activity of the clavicular portion of the pectorals major was higher at 44 compared to 56 degrees. There was a reduction in the activity of the sternocostal head of the pectorals major with increased bench angle, possibly a consequence of the reduced load.

The differences in muscle activation were explained by the fact that the different angles result in different movements around the shoulder joint. The flat bench results in more so-called horizontal adduction (the arms move from the side towards the middle of the body). The incline results in more flexion (the arms move upwards).13

Paractical application

  • Optimal activation of the clavicular head of the pectorals major (“upper chest”) may happen with the bench set between 40 and 55 degrees. A simple way to apply this information is to visually gauge the setting that results in a 45 degree angle and then integrate that setting plus the setting right below and the setting right above.
  • Higher activation of the sternocostal head of the pectorals major (“lower chest”) may happen with the flat or decline bench due to different movements around the shoulder joint and the ability to use higher loads.

Upper Back

This study compared muscle activation between a close-grip lat pulldown (a triangle handle), lat pulldown with a narrow supinated (underhand) grip, wide-grip lat pull to the chest and wide-grip lat pulldown to behind the neck. The two wide grips placed greater emphasis on the latissimus dorsi and the teres major (a small muscle running from the shoulder blade to the top of the upper arm), while the two close grips placed more emphasis on the posterior deltoids and pectorals major.6 The reason for the high degree of latissimus dorsi activation during the wide-grip lat pulldown variations is that these grips allow the latissimus dorsi to perform all of its three functions – shoulder extension, shoulder adduction and shoulder internal rotation.7 The close-grip lat pulldowns allow the posterior deltoids to perform one of its major functions, shoulder hyperextension (pulling the arm behind anatomical neutral, i.e., when the elbow moves behind the rib cage).8

Another study measured latissimus dorsi activation two centimeters from the outer edge of the latissimus dorsi and 10 centimeters medially from the first electrode. A close-grip front and wide-grip front and back lat pulldown were used. The wide-grip front lat pulldown was the most effective version to target the lateral latissimus dorsi.9

Interestingly, a seated row (neutral grip with six inches between the hands may increase latissimus dorsi activation above the levels of wide-grip pulldowns (front and back). Seated rows also increased rhomboid and middle trapezius activation beyond both versions of the pulldown. Actively “retracting the scapula” does not appear to increase rhomboid and middle trapezius activation.20

Practical application

  • Use wide-grip lat pulldowns to the front to target the lateral aspects of the latissimus dorsi.
  • Use close-grip lat pulldowns to target the posterior delts.
  • Use seated rows (wide grip) to target the rhomboids and middle trapezius.
  • Just pull naturally, but make sure to get full range of motion; there’s no need to “actively squeeze.”

Arms

Few body parts receive as much attention as the arms. Our interest includes, but is certainly not limited to, how to “peak” the biceps.

Fine-tuning the activation of the three biceps muscles2,14,15

  • The lateral portion of the long head is preferentially activated during elbow flexion and during incline curls.
  • The medial portion of the long head is preferentially activated during forearm supination (bring the forearm to the palms-up position).
    • There is preferential activation of the short head of the biceps during supination at 120 degree elbow angles.
  • The biceps brachii, in general, is more easily activated during slow lowering and lifting.
  • The brachialis is more easily activated during isometric actions and with the forearm in the palms down position.

Fine-tuning the activation of the three triceps muscles16,17

  • The medial head is active in almost any form of triceps extension exercise, including dumbbell kickbacks.
  • Activation of the long head of the triceps muscle is greatest with combined elbow and shoulder extension and or when the load is heavy – 4 to 8 repetitions per set.
  • The lateral head is recruited in dumbbell kickbacks.

Practical application

  • Target the long head and short head of the biceps with incline curls, making sure to finish with the pinky higher than the thumb (this is supination).
  • Target the brachialis by including isometric holds and reverse curls, including Zottman curls.
  • Target the medial head of the triceps – for example, with close-grip bench presses.
  • Target the long head of the triceps with heavy pullovers.
  • Target the lateral head of the triceps with dumbbell kickbacks (try to do the exercise with two dumbbells at a time).

References

  1. Can you peak your biceps? SkinnyBulkUp.com. Available at: http://skinnybulkup.com/biceps-peak/. Accessed March 5, 2014.
  2. Antonio J. Nonuniform response of skeletal muscle to heavy resistance training: can bodybuilders induce regional muscle hypertrophy? J Strength Cond Res. 2000;14(1):102-13.
  3. Riemann BL, Limbaugh GK, Eitner JD, Lefavi RG. Medial and lateral gastrocnemius activation differences during heel-raise exercise with three different foot positions. J Strength Cond Res. 2011 Mar;25(3):634-9.
  4. Paton ME, Brown JM. Functional differentiation within latissimus dorsi. Electromyogr Clin Neurophysiol. 1995 Aug-Sep;35(5):301-9.
  5. Stone MH, Stone M, Sands WA. Physical and physiological adaptations to resistance training. In: Principles and Practice of Resistance Training. Champaign, IL: Human Kinetics. 2007:216.
  6. Signorile JF, Zink AJ, Szwed SP. A comparative electromyographical investigation of muscle utilization patterns using various hand positions during the lat pull-down. J Strength Cond Res. 2002 Nov;16(4):539-46.
  7. Latissimus dorsi. E-Hand.com. Available at: http://www.eatonhand.com/mus/mus045.htm. Accessed March 5, 2014.
  8. Deltoid. ExRx.net. Available at: http://www.exrx.net/Muscles/DeltoidPosterior.html. Accessed March 5, 2014.
  9. Wills R, Signorile JF, Perry A, Tremblay L, Kwiatkowski K. Differences in EMG activity due to handgrip position during the lat pulldown. Med Sci Sports Exerc. 1994;26(5):S20.
  10. Kinakin K. Linking muscles to exercise movement. In: Optimal Muscle Training. Champaign, IL: Human Kinetics. 2004:48.
  11. Zebis MK, Skotte J, Andersen CH, et al. Kettlebell swing targets semitendinosus and supine leg curl targets biceps femoris: an EMG study with rehabilitation implications. Br J Sports Med. 2013 Dec;47(18):1192-8.
  12. Glass SC, Armstrong T. Electromyographical activity of the pectoralis muscle during incline and decline bench press. J Strength Cond Res. 1997;11(3):163-7.
  13. Trebs AA, Brandenburg JP, Pitney WA. An electromyography analysis of 3 muscles surrounding the shoulder joint during the performance of a chest press exercise at several angles. J Strength Cond Res. 2010 Jul;24(7):1925-30
  14. Sale D. Neural adaptation to strength training. In: Komi PV, ed. Strength and Power in Sport. Oxford; Boston: Blackwell Scientific Publications; Champaign, IL: Human Kinetics Books, distributor. 1992:249-265.
  15. Kinakin K. Linking muscles to exercise movement. In: Optimal Muscle Training. Champaign, IL: Human Kinetics. 2004:39.
  16. Davidson AW, Rice CL. Effect of shoulder angle on the activation pattern of the elbow extensors during a submaximal isometric fatiguing contraction. Muscle Nerve. 2010 Oct;42(4):514-21.
  17. Kinakin K. Linking muscles to exercise movement. In: Optimal Muscle Training. Champaign, IL: Human Kinetics. 2004:41.
  18. Irish SE, Millward AJ, Wride J, Haas BM, Shum GLK. The effect of closed-kinetic chain exercises and open-kinetic chain exercises on the muscle activity of vastus medialis oblique and vastus lateralis. J Strength Cond Res. 2010 May;24(5):1256-62.
  19. O’Sullivan SP, Popelas CA. Activation of vastus medialis obliquus among individuals with patellofemoral pain syndrome. J Strength Cond Res. 2005 May;19(2):302-4.
  20. Lehman GJ, Buchan DD, Lundy A, Myers N, Nalborczyk A. Variations in muscle activation levels during traditional latissimus dorsi weight training exercises: An experimental study. Dyn Med. 2004 Jun 30;3(1):4.
  21. Kendall FP, McCreary EK, Provance PG. Trunk muscles, strength tests and exercises. In: Muscles: Testing and Function with Posture and Pain. 4th ed. Baltimore, MD : Lippincott Williams & Wilkins. 1993.
  22. Vera-Garcia FJ, Moreside JM, McGill SM. Abdominal muscle activation changes if the purpose is to control pelvis motion or thorax motion. J Electromyogr Kinesiol. 2011 Dec;21(6):893-903.
  23. Lehmann GJ, McGill SM. Quantification of the differences in electromyography activity magnitude between the upper and lower portions of the rectus abdominal muscle during selected trunk exercises. Phys Ther. 2001 May;81(5):1096-101.
  24. Clark KM, Holt LE, Sinyard J. Electromyographic comparison of the upper and lower rectus abdominis during abdominal exercises. J Strength Cond Res. 2003 Aug;17(3):475-83.
  25. Sarti MA, Monfort M, Fuster MA, Villaplana LA. Muscle activity in upper and lower rectus abdominis during abdominal exercises. Arch Phys Med Rehabil. 1996 Dec;77(12):1293-7.
  26. Marchetti PH, Kohn AF, Duarte M. Selective Activation of the rectus abdominis muscle during low intensity and fatiguing tasks. J Sports Sci Med. 2011 Jun 1;10(2):322-7.
  27. Duncan M. Muscle activity of the upper and lower rectus abdominis during exercises performed on and off a Swiss ball. J Bodyw Mov Ther. 2009 Oct;13(4):364-7.
  28. Signorile JF, Applegate B, Dugue M, Cole N, Zink A. Selective recruitment of the triceps surae muscles with changes in knee angle. J Strength Cond Res. 2002 Aug;16(3):433-9.

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