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A much discussed topic in the diving medicine community, we still can't say for certain, but it seems we're homing in on consensus.
The old standard was 13 METs, largely established/championed by the eminent diving medicine cardiologist Fred Bove, MD, PhD. However, several years ago some authoritative diving medicine cardiologists suggested that while a diver who can attain 12-13 METS is "good to go" in any sport diving activity, those who can achieve ~60% of that (~6-7 METS), the equivalent of walking 2 miles in <25 mins, should be able to safely dive in most rec diving situations. They added that at that at level of fitness could still put divers at risk should they find themselves in the extremes of diving in terms of cold, current, rescue, etc., situations.
The latest research appears consistent with this position:
1. "Diving Hyperb Med. 2014 Jun;44(2):74-8.
Exercise intensity inferred from air consumption during recreational scuba diving.
Buzzacott P1, Pollock NW2, Rosenberg M3.
Author information 1Adjunct Lecturer, School of Sport Science, Exercise and Health, the University of Western Australia, Perth, Australia, Marie Curie Research Fellow, Laboratoire Optimisation des Régulations Physiologiques, Université de Bretagne Occidentale, UFR Sciences et Techniques, 6 avenue Le Gorgeu, CS 93837, Brest Cedex 3, France, Phone: +33-(0)2-9801-6235, E-mail: peter.buzzacott@uwa.edu.au.2Research Director, Divers Alert Network, Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, USA.3Director of the Health Promotion Evaluation Unit, School of Sport Science, Exercise and Health, the University of Western Australia, Perth, Australia.
Abstract
INTRODUCTION: Episodic exercise is a risk factor for acute cardiac events and cardiac complications are increasingly recognized in fatalities during recreational scuba diving. What is not known is the exercise intensity involved in typical recreational diving.
METHODS: This study used pre- to post-dive gas cylinder pressure drop to estimate air consumption and, from that, exercise intensity during recreational dives. Dive profiles were captured electronically and divers self-reported cylinder pressure changes, perceived workload, thermal status and any problems during dives. Mean surface air consumption (SAC) rate per kg body weight and mean exercise intensity (reported in metabolic equivalents, MET multiples of assumed resting metabolic rate of 3.5 mL·kg⁻¹·min⁻¹) were then estimated. Data are reported as mean ± standard deviation.
RESULTS: A total of 959 recreational air dives (20 ± 9 meters' sea water maximum depth; 50 ± 12 min underwater time) by 139 divers (42 ± 10 y age; 11 ± 10 y of diving; 12% smokers; 73% male) were monitored. Problems were reported with 129/959 dives: buoyancy (45%), equalization (38%), rapid ascent (10%), vertigo (5%) and other (2%). Assuming a 10% overestimate due to cylinder cooling and uncontrolled gas loss, the estimated exercise intensity associated with monitored dives was 5 ± 1 MET. Mean ± 2SD, or 7 MET, captures the effort associated with the vast majority of dives monitored.
CONCLUSIONS: Our estimates suggest that uncomplicated recreational dives require moderate-intensity energy expenditure to complete, with a 7-MET capacity generally adequate. Higher levels of aerobic fitness are still strongly recommended to ensure ample reserves. Further research is needed to quantify energetic demands of recreational diving during both typical and emergent events in both experienced and less experienced divers."
2. Diving Hyperb Med. 2014 Sep;44(3):174.
Measuring aerobic fitness in divers.
Pollock NW1, Buzzacott P2.
Abstract
The editorial by Bosco, Paoli and Camporesi in the last issue of this journal provides an interesting overview of some of the factors that are either known or suspected to be important in the physiological health of divers. The part pertinent to our paper concerns the meaning and use of metabolic equivalents (MET). Our goal was to estimate the metabolic effort required for a substantial sample of recreational dives. Computing MET values based on an assumed resting oxygen consumption rate of 3.5 millilitres of oxygen per kilogram body mass per minute is well established. Most pointedly, MET is used in the Recreational Scuba Training Council (RSTC) Guidelines for Recreational Scuba Diver's Physical Examination found in the Medical Statement documentation. Given the increasingly widespread use of the RSTC assessment, it makes the most sense to be consistent. Concerns over whether or not a more appropriate index value could be used are moot. Anyone wishing to compute a different base for 1.0 MET can simply crossmultiply and divide. The question to be answered is not what level of aerobic capacity is desirable for divers, the answer to that is the higher the better. The critical question is what constitutes a reasonable minimum threshold aerobic capacity consistent with operational safety. The authors mention the often invoked 13 MET capacity identified as a threshold for US Navy divers. What is typically ignored, however, is the fact that the Navy has far more applicants for dive school than posts to be filled, making very stringent selection standards feasible even if not truly operationally necessary. It is not at all clear that this is a reasonable threshold for the broader diving community. Despite this, the RSTC documentation adheres to the traditional position. "Formalized stress testing is encouraged if there is any doubt regarding physical performance capability. The suggested minimum criteria for stress testing in such cases is at least 13 METS [sic]. Failure to meet the exercise criteria would be of significant concern." This is contrary to the available data. A review of 14 studies in which the aerobic capacity of divers was measured found that mean aerobic fitness ranged from 37-57 mL∙kg⁻¹∙min⁻¹ (10.6-16.3 MET). The lowest individual scores were below 5.0 MET. The threshold of 13 MET was exceeded by the group mean in only six of the 14 studies described. This certainly does not support 13 MET as a meaningful threshold for participation. Our current work was intended as a simple effort to begin to assess the aerobic demands of recreational diving. It is our hope to promote discussion that is willing to risk the heresy of challenging conventional wisdom and to stimulate additional research. We certainly agree with the authors and feel strongly that enhanced in-water evaluation of physical fitness is desirable to establish diver readiness. We would not, however, refer to this as a "medical examination" since it is likely that it will largely be dive professionals and not clinicians that conduct the evaluations.
Regards,
DocVikingo
The old standard was 13 METs, largely established/championed by the eminent diving medicine cardiologist Fred Bove, MD, PhD. However, several years ago some authoritative diving medicine cardiologists suggested that while a diver who can attain 12-13 METS is "good to go" in any sport diving activity, those who can achieve ~60% of that (~6-7 METS), the equivalent of walking 2 miles in <25 mins, should be able to safely dive in most rec diving situations. They added that at that at level of fitness could still put divers at risk should they find themselves in the extremes of diving in terms of cold, current, rescue, etc., situations.
The latest research appears consistent with this position:
1. "Diving Hyperb Med. 2014 Jun;44(2):74-8.
Exercise intensity inferred from air consumption during recreational scuba diving.
Buzzacott P1, Pollock NW2, Rosenberg M3.
Author information 1Adjunct Lecturer, School of Sport Science, Exercise and Health, the University of Western Australia, Perth, Australia, Marie Curie Research Fellow, Laboratoire Optimisation des Régulations Physiologiques, Université de Bretagne Occidentale, UFR Sciences et Techniques, 6 avenue Le Gorgeu, CS 93837, Brest Cedex 3, France, Phone: +33-(0)2-9801-6235, E-mail: peter.buzzacott@uwa.edu.au.2Research Director, Divers Alert Network, Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, USA.3Director of the Health Promotion Evaluation Unit, School of Sport Science, Exercise and Health, the University of Western Australia, Perth, Australia.
Abstract
INTRODUCTION: Episodic exercise is a risk factor for acute cardiac events and cardiac complications are increasingly recognized in fatalities during recreational scuba diving. What is not known is the exercise intensity involved in typical recreational diving.
METHODS: This study used pre- to post-dive gas cylinder pressure drop to estimate air consumption and, from that, exercise intensity during recreational dives. Dive profiles were captured electronically and divers self-reported cylinder pressure changes, perceived workload, thermal status and any problems during dives. Mean surface air consumption (SAC) rate per kg body weight and mean exercise intensity (reported in metabolic equivalents, MET multiples of assumed resting metabolic rate of 3.5 mL·kg⁻¹·min⁻¹) were then estimated. Data are reported as mean ± standard deviation.
RESULTS: A total of 959 recreational air dives (20 ± 9 meters' sea water maximum depth; 50 ± 12 min underwater time) by 139 divers (42 ± 10 y age; 11 ± 10 y of diving; 12% smokers; 73% male) were monitored. Problems were reported with 129/959 dives: buoyancy (45%), equalization (38%), rapid ascent (10%), vertigo (5%) and other (2%). Assuming a 10% overestimate due to cylinder cooling and uncontrolled gas loss, the estimated exercise intensity associated with monitored dives was 5 ± 1 MET. Mean ± 2SD, or 7 MET, captures the effort associated with the vast majority of dives monitored.
CONCLUSIONS: Our estimates suggest that uncomplicated recreational dives require moderate-intensity energy expenditure to complete, with a 7-MET capacity generally adequate. Higher levels of aerobic fitness are still strongly recommended to ensure ample reserves. Further research is needed to quantify energetic demands of recreational diving during both typical and emergent events in both experienced and less experienced divers."
2. Diving Hyperb Med. 2014 Sep;44(3):174.
Measuring aerobic fitness in divers.
Pollock NW1, Buzzacott P2.
Abstract
The editorial by Bosco, Paoli and Camporesi in the last issue of this journal provides an interesting overview of some of the factors that are either known or suspected to be important in the physiological health of divers. The part pertinent to our paper concerns the meaning and use of metabolic equivalents (MET). Our goal was to estimate the metabolic effort required for a substantial sample of recreational dives. Computing MET values based on an assumed resting oxygen consumption rate of 3.5 millilitres of oxygen per kilogram body mass per minute is well established. Most pointedly, MET is used in the Recreational Scuba Training Council (RSTC) Guidelines for Recreational Scuba Diver's Physical Examination found in the Medical Statement documentation. Given the increasingly widespread use of the RSTC assessment, it makes the most sense to be consistent. Concerns over whether or not a more appropriate index value could be used are moot. Anyone wishing to compute a different base for 1.0 MET can simply crossmultiply and divide. The question to be answered is not what level of aerobic capacity is desirable for divers, the answer to that is the higher the better. The critical question is what constitutes a reasonable minimum threshold aerobic capacity consistent with operational safety. The authors mention the often invoked 13 MET capacity identified as a threshold for US Navy divers. What is typically ignored, however, is the fact that the Navy has far more applicants for dive school than posts to be filled, making very stringent selection standards feasible even if not truly operationally necessary. It is not at all clear that this is a reasonable threshold for the broader diving community. Despite this, the RSTC documentation adheres to the traditional position. "Formalized stress testing is encouraged if there is any doubt regarding physical performance capability. The suggested minimum criteria for stress testing in such cases is at least 13 METS [sic]. Failure to meet the exercise criteria would be of significant concern." This is contrary to the available data. A review of 14 studies in which the aerobic capacity of divers was measured found that mean aerobic fitness ranged from 37-57 mL∙kg⁻¹∙min⁻¹ (10.6-16.3 MET). The lowest individual scores were below 5.0 MET. The threshold of 13 MET was exceeded by the group mean in only six of the 14 studies described. This certainly does not support 13 MET as a meaningful threshold for participation. Our current work was intended as a simple effort to begin to assess the aerobic demands of recreational diving. It is our hope to promote discussion that is willing to risk the heresy of challenging conventional wisdom and to stimulate additional research. We certainly agree with the authors and feel strongly that enhanced in-water evaluation of physical fitness is desirable to establish diver readiness. We would not, however, refer to this as a "medical examination" since it is likely that it will largely be dive professionals and not clinicians that conduct the evaluations.
Regards,
DocVikingo
