EXERTION AND FITNESS CONSIDERATIONS IN DIVING
Fitness is a generic term that represents the person’s ability to meet the challenges of a particular
task or activity. Fitness for an executive position may require the ability to concentrate and utilize utmost cognitive activities for sustained periods. For workers, fitness may require the ability to move, lift, and carry heavy objects for eight or more hours a day. For the athlete, fitness implies that the participant is able to meet the exercise, mobility, strength, and intellectual demands that the particular sport requires. Metabolic equivalents (METS) is a measure used to assess fitness for exercise.3
The subject of fitness for diving generates several paradoxes. First, there is no disagreement that divers should have a level of fitness consistent with the anticipated physical challenges of the dive. Under ideal conditions, the dive could be less energy demanding than walking at a slow pace. Ideal conditions include diving off a boat, clear water, warm water, no currents, swells, or waves, and a descending line for aiding with ascents and descents. This type of diving requires a metabolic equivalent (METS) of seven to eight.4 The second paradox is if an emergency situation arises, extreme energy demands may be required. For such situations, total effort may be required for extrication. For this reason, 12-13 METS has been advocated as target level for scuba divers.5-6 This is unrealistically high for the typical sports diver and is a level of fitness achieved in Navy SEAL teams personnel among others. Consequently, the metabolic activity of the anticipated activity must be factored into making decisions about diving. This is where the appreciation of stress-stimulus/reaction-response challenges becomes crucial in diving activities and will be further developed in ensuing chapters.
With respect to physical stresses of the dive, each phase of the dive requires different exertion levels (Figure 4). During the surface/water entry phase, the greatest exertion levels as exhibited by elevated heart rates occur especially with shoreline entry dives. Exertional stresses for donning exposure suits, carrying diving equipment to the shoreline, making the beach entry and transiting the surf zone are the highest during any time of a dive profile. Once the surf zone is surpassed, swimming to the dive site can be another cause of exertion, especially if currents or swells are encountered. With descent, the second phase of the dive begins and exertional stresses are markedly decreased. Descent can be aided by releasing air from the buoyancy compensator to achieve negative buoyancy and essentially sink to the bottom. A non-exertional stress during this phase of the dive is equilibration of pressure (i.e. clearing the ears) in the middle ear spaces.
During the bottom phase, slow swimming movements reduce exertion. If neutrally buoyant, and comfortable in the water, this phase of the dive becomes the least exertional of the four phases. This is the reason scuba diving is not considered a good “cardio” exercise.7 However, if there is a current, energy may be expended to swim against it so that at the turn around point (recommended aft er ⅓ of the scuba tank air supply is consumed), swimming back to the starting point minimizes exertion by drift ing with the current. During the ascent phase energy expenditures increase. By achieving positive buoyancy with addition of air to the buoyancy compensator, exertion to ascend can be minimized. However, energy requiring activities as mentioned in the surface/water entry phase will occur in order to return to the starting point (i.e. before donning diving equipment).
The reason fitness is necessary for scuba diving is that if something goes wrong, the diver needs to have enough energy reserve to extricate himself/herself from the unforeseen event. Whereas, a diver may be able to sustain mild to moderate levels of exertion for long periods, with full exertion, exhaustion can occur in a matter of a few seconds as struggling in an entanglement (Figure 5). Energy expenditures can be substantially reduced by diving with the optimal conditions discussed above. Through planning and common sense, every effort, regardless of the diving environment, should be made to reduce energy expenditures during the dive.
MEASURING FITNESS
Can fitness be quantified? Both physiological and performance measures can be used to assess fitness. Heart rate measurements with exercise is a simple physiological testing method for determining fitness. The ability to do sustained exercise at 75 to 80% of the maximal recommended heart rate is an easy method to measure. Remember, with aging,the maximal recommended heart rate decreases according using the formula 220 minus age, but this math underestimates an older person’s exercise capability.8 For example using above formula, the recommended maximum heart rate for a 60-year-old diver would be 220 – 60 or 160 beats per minute; 75% of this is 120. Consequently, an “ideal” cardio workout for this age would be an activity that increases the heart rate to 120. A second physiological measure for fitness is to use the metabolic equivalent approach as discussed previously.
Various performance testing procedures can be used to test fitness and several are designed for water related activities. A good starting point for someone who wants to begin and continue to scuba dive is being able to meet the Boy Scouts of America Life Saving Merit badge requirements (see Chapter 14). Cooper generated “The 12-minute Swim Test for Assessing Cardiorespiratory Endurance.”9 The test consists of measuring the swimming distance covered in 12 minutes and rates it in five categories from very poor to excellent, in six age categories (from 12-19 and to 60 and over) and whether male or female. To scuba dive we recommend at least meeting the “fair” rating for the particular age group and sex.
The International Association of Diving Rescue Specialists Watermanship Testing (IADRS) is another approach to measuring fitness in the aquatic environment.10-11 It consists of five exercises including a timed surface swim, snorkel swim with fins, treading water, rescue tow with fins, and object retrieval from nine feet of water. The first four items are timed and graded from incomplete (equivalent to 0 points) to five points. According to IARDS standards 12 points (of a maximum of 20 points) plus object retrieval from 10 feet of water are required to meet their standards.Final considerations about the subject of fitness for scuba diving are comfort in the water and familiarity with the diving equipment. The ability to be relaxed in water helps mitigate lack of swimming ability and this coupled with judgement and experience can compensate for this deficiency (see Chapter 12). A runner with mediocre water skills is likely to become an adept swimmer after donning a pair of fins if comfortable in the water. Fitness also implies familiarity with diving equipment. Those who do not scuba dive regularly should be re-oriented to diving activities with minimally challenging dives preferably with dive guide supervision during their initial resumption of this sport.
REFERENCES
1. Strauss MB, Aksen IV. Diving Science : Essential Physiology and Medicine for Divers. Champaign, IL:Human Kinetics;2004.
2. Selye H. The Stress of Life. New York: McGraw Hill. 1956.
3. Jette M, Sidney K, Blumchen G. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clin Cardiol. 1990; 13(8):555-565.
4. Pollock NW. Aerobic fi tness and underwater diving. Diving Hyperb Med. 2007; 37(3):118-123.
5. Bove AA. Medical aspects of sport diving. Med & Science in Sports & Exercise. 1996; 28(5):591-595.
6. Bove AA. The cardiovascular system and diving risks. Undersea Hyperb Med. 2011; 38(4):261-269.
7. MacMillan A. Is SCUBA diving a good workout? Fitness Coach. 2014. www.outsideonline.com.
8. Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am College Cardiol. 2001; 37(1):153-156.
9. Cooper KH. The Aerobics Programs for Total Well-Being. New York: Bantam Books. 1992.
10. 11. I.A.D.R.S. Annual Watermanship Test. http://www.iadrs.org/media/IADRS_Watermanship_Test.pdf. Strauss MB, Busch JA, Miller SS. SCUBA in older aged divers. Wound Care & Hyperb Med. 2013;
4(3):27-38.
Source: Diving Science ... Revisited, An Innovative Approach to the Medical Challenges of Diving by Michael B. Strauss, MD
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