PET/CT imaging identifies specific skeletal muscles involved in this classic Yoga exercise.

1. The Physiology of Sun Salutation (Surya amaskar)
Peeyush Bhargava M.D, ABIHM
www.vedic-healing.com
Introduction:
Sun Salutation or Surya Namaskar (SN) is a classic yoga exercise consisting of 12 asanas
preformed sequentially, and synchronized with breathing. It is considered a
comprehensive and ideal practice for physical and spiritual wellbeing. SN is performed as
a prayer to the Sun, ideally at sunrise and in open air, facing east [1]. It has aerobic and
dynamic components, and has been shown to improve strength, body composition, and
general body endurance [2,3]. Performing 6-8 rounds will achieve the energy expenditure
of light exercise intensity, and a 10 minute practice may improve cardio-respiratory
fitness in unfit or sedentary individuals [4, 5].

2. We attempted to identify the skeletal muscles involved in SN by visualizing F-18 FDG
hypermetabolism on PET/CT imaging. F-18 FDG PET/CT imaging is the standard of
clinical care in patients with malignancies [6]. Typically, 10 mCi of F-18 FDG is injected
IV and whole body PET/CT images are acquired 60 minutes later. Cancer cells have
higher rate of glucose utilization and so cancerous lesions are identified on the images as
foci of increased uptake or hypermetabolism. Patients have to fast for at least 6-8 hrs and
are asked to avoid physical exertion 24 hrs before to after the scan [7]. Artifactual skeletal
muscle uptake is frequently seen on the images and correlates well with physical activity
during the uptake period [8]. PET imaging has been used to study skeletal muscle glucose
metabolism [9, 10].
After the intravenous administration of 8.7 mCi of F-18 FDG a healthy male volunteer
performed 15 rounds of SN in 45 minutes. These were performed at a moderate pace of
30-45 seconds per cycle, and in sets of five cycles with intermittent rest. He then
underwent whole body PET/CT imaging on Siemens Biograph PET/CT scanner. The
PET images were acquired at 3 min per bed position, in 3D mode, from the top of the
head to the tips of the toes. Corresponding CT images were acquired at a low dose, and
without any oral or intravenous contrast. CT based attenuation correction was applied and
images were reconstructed and interpreted in three orthogonal planes.

3. Figure 1: Anterior (A) and left lateral view (B) of the whole body FDG PET/CT images
showing intense uptake in bilateral shoulders and anterior abdominal muscles (arrows).
Physiologic uptake is seen in the brain, liver, kidneys, and the urinary bladder.

4. The images show most intense skeletal muscle uptake in both shoulders and anterior
abdominal muscles (Figure 1). It is clear that with most intense uptake in these regions on
PET/CT imaging after performance of 15 rounds, practice of SN will exercise
predominantly the shoulders and the anterior abdominal muscles. The fused PET/CT
images (Figure 2) localize the uptake to the following individual muscles bilaterally:
deltoid, infraspinatus, triceps, serratus anterior, rectus abdominis, and tibialis anterior.
Physiologic uptake is seen in the brain, the lymphoid tissue and vocal cords in the neck,
liver and myocardium, and intense activity is seen from renal excretion of the tracer in
the kidneys, ureter, and the urinary bladder.
Figure 2: Fused PET/CT images localize FDG uptake to deltoid and infraspinatus (arrow
and arrow head respectively in A); triceps and serratus anterior muscles (arrow and arrow
head respectively in B); rectus abdominis in C, and tibialis anterior muscles in D.

5. Sun salutation has been well described in the yogic literature [1], but a recent search of
modern scientific literature revealed only 7 articles when “sun salutation” was used as the
search word and only 4 articles when “surya namaskar” was used for search.
The twelve steps involved in this exercise are well described in several papers using
illustrations [1, 2,3]. These steps involve alternate flexion and extension of the spine in
association with inspiration and expiration, respectively. This can be expected to be seen
on PET/CT imaging as increased uptake in the anterior abdominal muscles (flexion) and
the paraspinal muscles of the back (extension). We found more intense uptake in the
rectus abdominis muscle, as compared to the paraspinal extensors. This is in contrast with
Sinha et al who showed that the backward bending poses have greater oxygen demand [2].
Several SN steps involve weight bearing in the shoulders and arm extension to push up
the body weight. These are seen as increased uptake in the deltoid, infraspinatus, triceps,
and serratus anterior muscles. Flexion and extension at the hip joint was not seen as
increased uptake in any muscles. Dorsiflexion at the ankle is seen as intense uptake in
bilateral tibialis anterior muscles. This case study identifies the skeletal muscles involved
in SN, seen as increased uptake of F-18 FDG on PET/CT imaging. A baseline resting
whole body FDG PET/CT scan without the intervention of SN could make this report
more convincing, but was avoided for the reason of limiting radiation exposure from an
additional radio-isotope injection and CT imaging study. It does not address the questions
about how exercising these specific muscles bring about the known health benefits, but
shows that imaging of F-18 FDG using PET/CT is a viable method in identifying muscle
recruitment during yoga exercises.

6. References:
1. Saraswati SS. Surya Namaskar. Asana Pranayama Mudra Bandha, 3rd edition. New
Delhi: Bihar School of Yoga; 1996. p. 159-172.
2. Sinha B, Ray US, Pathak A, Selvamurthy W. Energy cost and cardiorespiratory
changes during the practice of Surya Namaskar. Indian J Physiol Pharmacol.
2004;48:184-90.
3. Bhutkar MV, Bhutkar PM, Taware GB, Surdi AD. How effective is sun salutation in
improving muscle strength, general body endurance and body composition? Asian J
Sports Med. 2011;2:259-66.
4. Sinha B, Ray US, Sinha TD. Physiological study of Surya Namaskar, a yogic practice.
Altern Ther Health Med. 2011;17:62-3.
5. Hagins M, Moore W, Rundle A. Does practicing hatha yoga satisfy recommendations
for intensity of physical activity which improves and maintains health and cardiovascular
fitness? BMC Complement Altern Med. 2007;7:40.
6. Poeppel TD, Krause BJ, Heusner TA, Boy C, Bockisch A, Antoch G. PET/CT for the
staging and follow-up of patients with malignancies. Eur J Radiol. 2009;70:382-92.
7. Basu S, Kwee TC, Surti S, Akin EA, Yoo D, Alavi A. Fundamentals of PET and
PET/CT imaging. Ann N Y Acad Sci. 2011;1228:1-18.
8. Shreve PD, Anzai Y, Wahl RL. Pitfalls in oncologic diagnosis with FDG PET
imaging: physiologic and benign variants. Radiographics. 1999;19:61-77.
9. Selberg O, Müller MJ, van den Hoff J, Burchert W. Use of positron emission
tomography for the assessment of skeletal muscle glucose metabolism. Nutrition.
2002;18:323-8.
10. Kelley DE, Price JC, Cobelli C. Assessing skeletal muscle glucose metabolism with
positron emission tomography. IUBMB Life. 2001;52:279-84.