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Abstract
Context: “Surya Namaskar” (SN) may be used as a need-based short-duration aerobic activity in a confined space to establish as a substitute of an equivalent routine physical training in challenging stressful conditions. Materials and Methods: Noninvasive oxygen-kinetics metabolic responses between SN and endurance work on bicycle ergometry (BE) were compared across different phases of maximal oxygen uptake percentage (%VO2 max). SN, comprising three complete rounds per min (36 beats/min of a metronome; SN consists of 12 poses per round), was performed rhythmically and continuously for 5 min to simulate an incremental BE test (25 watts/2 min at 60 rpm). Results: SN results in a significant (P < 0.05) greater increase of arteriovenous oxygen difference at 71%–80% VO2 max while keeping a low respiratory exchange ratio (P < 0.01 and 0.001) at 41%–80% VO2 max exercising state. Conclusions: SN could be an ideal form of aerobic exercise instead of BE.
Keywords: Dynamic yoga, incremental exercise test, maximal oxygen uptake percentage
How to cite this article: Introduction 
To ascertain strength–power capabilities, and fatigue resiliency under moderate intensity (MI) there is a prerequisite of a short-duration, aerobic activity in a confined space substituting traditional exercise regimes for the challenging stressful situation. Combat fitness is one of prerequisite to maintain regular physical fitness even in extreme adverse environmental conditions where exercise in open air is difficult such as Antarctica, cold and high altitude, hot desert, and microclimate in submarine and space. In these challenging conditions, Surya Namaskar (SN) could be a useful fitness substitute to maintain regular exercise regime.
SN or Sun Salutation, a component of Hatha yoga, consisting of a series of 12 postures (asanas), performed rhythmically with controlled breathing in one round without any pause in between and also involves both static and dynamic musculoskeletal stretching exercises recruiting the majority components of the spine, joints, and muscles of the body.[1],[2] The most common variation, i.e., Sun Salutation, can be practiced to achieve an aerobically intense effort (metabolic equivalents [METs] up to 7.4 with 80% maximal heart rate [HRmax], at the pace of 3 min per round)[3] by incorporating rapid transition jumps and full pushups in between asanas.[4]
In bicycle ergometry (BE), the exercise capacity at a specific level of workload is exerted immediately and solely on lower limb muscles unlike progressive increment disseminating among various groups of muscles in SN from 1st to successive rounds. Previously, at a similar level of exercise intensity (i.e., 41%–50% of VO2 max), the metabolic stress was reported to be greater in BE than SN.[5]
Although the reported research[5] was aimed at ≤50% VO2 max in terms of progressive work intensities; research beyond this level and focusing majorly the stroke volume (SV), cardiac output (Q), a-vO2 diff. response is still unavailable. Considering the same central and peripheral cardiovascular factors, the current study was aimed to compare SN and BE across low to exhaustive phases of exercise intensities.
Materials and Methods Study design
This study was self-control.
Subjects
The study was approved by the Institutional Ethical Committee (viz., Ref. No. IEC/DIPAS/A-4/2) considering the Helsinki Declaration of 1975, as revised in 2000. Seven (n = 7) physically fit men involved in routine physical training, and without any history of medication (mean age: 32.6 ± 1.97, years; height: 172.0 ± 7.09, cm; body weight: 76.8 ± 5.86, kg) were recruited. The subjects for this study were the defense personnel posted in DRDO.
Procedures
The volunteers have practiced SN adequately for over 2 years and performed SN comprising three complete rounds per min continuously for a total duration of 5 min by wearing a portable metabolic cart (START 200M Ergospirometer, MES, Poland) in a thermoneutral room. Each pose of SN [Figure 1] was standardized with each beat of a metronome set in 36 beats/min.
After 1 day of rest, a standard graded BE test (using Monark LC4 G3, Sweden) at an incremental workload of 25 watts/2 min at 60 rpm was conducted on the same volunteers till exhaustion.
Informed consent was obtained and noninvasive measurements of heart rate (HR) (by Polar H10, Finland) and VO2 max followed by minute ventilation (VE), Q, SV, arteriovenous oxygen difference, and respiratory exchange ratio (RER) were recorded. SN and BE were compared at similar maximal oxygen uptake percentage (%VO2 max) level.
Data analysis
Average VO2 max of SN practice (at the end of 5 min) and BE was recorded 34.0 ± 11.99 and 43.6 ± 13.63 ml/kg/min, respectively. Eight exercise intensities equivalent to an energy expenditure of 10%–80% VO2 max for light intensity (10%–20% and 21%–30%), MI (31%–40% and 41%–50%), high intensity (HI) (51%–60% and 61%–70%), and very HI (VHI) (71%–74% and 75%–80%) were evaluated both from SN and BE VO2 max (average). The parameters at different phases were compared keeping %VO2 max as constant. Two-factorial ANOVA while considering “exercise intensity” and “type of exercise” both as factors followed by Bonferroni's post hoc test was applied using SPSS (SPSS Statistics for Windows, version 27.0 IBM Corp., Armonk, N.Y., USA).
Results From the MI (31% VO2 max) onward, BE showed a tendency to overestimate HR, VE, Q, SV, and RER as evident by [Table 1]. SN results a significant (P < 0.05) greater increase in C (a-v) O2 at the VHI (71%–80% VO2 max) [Figure 2]a keeping lower RER values (P < 0.01, 0.001) between moderate and VHI (41%–80% VO2 max) [Figure 2]b.
Table 1: Comparison of heart rate, minute ventilation, cardiac output and stroke volume during Surya Namaskar and bicycle ergometry at different exercise intensities
Figure 2: Graphical representation of the comparison of the means of the effect of SN and BE on: (a) C(a-v)O2 (mL/100mL) and (b) RER at different exercise intensities. Values are (mean ± SEM) followed by One-way ANOVA. Level of significance: ***P < 0.001, **P < 0.01, * P < 0.05. SN: Surya Namaskar, BE: Bicycle ergometry, C(a-v)O2: Arterio-venous oxygen difference, RER: Respiratory exchange ratio Discussion At the initial phase, the higher values of the parameters in SN might be due to “muscle metaboreflex” caused by the forceful isometric contraction-induced accumulation of local metabolites,[5] attributing also similar SN and BE values at 31%–40% VO2 max as a carryover effect.
When exercise intensity has progressed into the higher side (41%–50% VO2 max onward); HR, VE, Q, and SV in BE was increased predominantly by muscle chemoreflex and “central command,” decreasing parasympathetic activity to the sinus node while activating central neuronal circuits.[6] In reports, SN practitioners hold a particular posture for 15–20 s followed by transitioning onto the next posture by the dynamic action of the muscles, thus causing cessation of the isometric contraction phase.[7] Moreover, muscle metaboreflex during SN at this phase, unable to cause further increment by controlling either parasympathetic or sympathetic efferent activity.[8]
During a specific muscle mass exercise, the venous O2 saturation value is higher than during whole-body exercise because skeletal muscle mitochondria can operate at a very low partial pressure of oxygen.[9] This low-deep venous O2 saturation allows O2 extraction to increase further and consequently, as a resultant effect of an induced O2 diffusion capacity by the involvement of slow type (i.e., Type I) muscle fibers during SN [Figure 2a].[10] Reducing blood flow to contracting muscle to regulate arterial pressure is also a causative factor of very low deep venous saturation.[11]
The amount of CO2 produced in BE was significantly exceeded that produced in SN due to strong ventilatory drive resulting from higher blood PCO2 produced at 41%–50% VO2 max causing a higher RER [Figure 2b]. Potentially, the increase in VE without an increase in O2 extraction (since Ca-vO2 difference changes slowly at the high intensities) might be an important reason to surge Q to meet the subjects' aerobic response in BE.[12] C (a-v) O2 (i.e., the difference in the O2 content between arterial and venous blood) represents the body's ability to oxygenate the blood. The greater the amount of O2extracted by the tissues, the greater the a-vO2 difference; therefore, higher a-vO2 difference resulted with exercise intensity as blood flow to the tissues increases, and hemoglobin dissociates more easily.
Adding arm exercise to ongoing leg exercise activities alters hemodynamic and neural responses than exercises involving only leg muscles at similar O2cost.[11] Therefore, collective perfusion of all of the active muscles might improve the overall limitation of Q on muscle blood flow and O2 delivery. The challenges to venous return and cerebral blood flow are associated with different postures, as blood pressure changes during head-down poses of SN; it also, plays a key role in the cardiovascular response.[11] Possibly, the complex interactions between the sympathetic nervous system and the microcirculation during upright posture versus the horizontal position (i.e., baroreflex resetting thereby altering perfusion of central nervous system and vital organs) facilitate high levels of systemic O2 extraction and permit just enough sympathetic control of blood flow (i.e., sympathetic vasoconstriction) to the contracting muscles to regulate blood pressure.[11]
SN meets nearly all the criteria of the American College of Sports Medicine's current guidelines[13] in terms of type of exercise (viz., aerobic, resistance, flexibility, and proprioceptive and neuromotor exercise) with purposive frequency, intensity, time, and volume. SN could be performed in multiple sessions of ≥10 min or could be slowed down by holding a static stretch for 10–30 s also recommended for most adults.
Practicing SN at 51%–60% VO2 max (i.e., at 7 METS) for ≥25–50 min/day on ≥3–5 day/week reaches the weekly goal of ACSM's criteria (i.e., 150 min/week of total exercise volume and energy expenditure of ≥500–1000 MET. min/week or ~1400 kcal/week) for cardiorespiratory fitness in adults.
However, more appropriately, as per relative measure of intensity, middle-aged (40–64 years) person working at six METs (i.e., at 41%–50% VO2 max of SN) may be exercising at a vigorous to maximal intensity as per HRmax, whereas a younger person working at the same absolute intensity will be exercising moderately.[14]
On the other hand, practicing SN for ≥20–40 min/day on ≥3–5 day/week at 61%–70% VO2 max (i.e., at 8 METS), meets directly the criteria for young adults (20–39 years) as vigorous-intensity cardiorespiratory exercise training reaching the recommended volume of ≥75 min/week.
In accordance with Mody,[3] time to exhaustion in SN in current study is significantly lower than BE at higher intensities, yet we studied purposely only for 5 min at 3 rounds/min paces. Again, well-trained athletes require “near-maximal” (i.e., 95%–100% VO2 max) training intensities to improve VO2 max. On the other hand, in moderately trained athletes, 70%–80% VO2 max seemed to provide a sufficient stimulus of enhancement.[15] Therefore, SN at similar intensity range could be ideal to be incorporated into high-intensity interval training (HIIT) regimen for enhancing VO2 max.
Limitations of the study
Special recruitment restricted low sample size and simple methodology was the key limiting factor.
Clinical implications
This study enables a new approach of easily implementable, whole-body moderate-intensity workout at any confined situation in minimum requiring space without any equipment during any challenging conditions.
Conclusions The practice of SN demands less metabolic stress with a widespread workload distributed among various muscle groups thereby restraining blood flow and other metabolites accumulation in a single active muscle eventually causing higher peripheral O2 extraction capacity. Therefore, SN could be another form of aerobic exercise with equivalent BE-VO2 kinetics, and a lower RER of SN could be utilized for short-duration aerobic training.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References 
Correspondence Address:
Mantu Saha
DIPAS, DRDO, New Delhi
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/ijoy.ijoy_8_22
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