THE HSE GUIDANCE STATES that a diver with a VO2Max equal to or greater than 45 can be issued with a fitness-to-dive certificate, while one with a VO2Max of less than 40 should be certified as “unfit”.
Figure 4 – Oxygen consumption relative to exercise intensity.
Source: DAN Recreational Diving Fatalities Workshop 2010.
For those with a VO2Max between 40 and 45 the doctors should conduct an individual risk-assessment, taking account of other findings and type of diving activity.
Based on this assessment, they can then issue a three-month time-limited certificate or a full 12-month certificate restricted to specific diving activities, such as no-saturation diving or no diving below 50m.
There are two things to consider here. The first is that a VO2Max of 45 is a high level of fitness. It’s equivalent to running at 9mph (6 min/mile), cycle-racing, competition canoeing, sparring in a boxing ring or playing a competitive squash match.
The second is that, as shown in figure 6, VO2Max tends to vary with age and gender. So a score of 38 might be considered good for a male of 50-plus, but merely average for a 25-year-old male.
A VO2Max of 45, required for a pass on the HSE medical, is considered average fitness for an 18-year-old male but would be a good level for a 48-year-old male and excellent for a 52-year-old man.
The same passing level of VO2Max would be good for an 18-year-old female and would require an excellent level of fitness for any woman of 40 or older.
So is a VO2Max of 45 unrealistically high, and does it unfairly penalise older or female divers?
To answer the first question, I set up a rescue scenario with Tim Clements from the Vobster inland dive-site. We put a Suunto heart-rate monitor on the rescuer and filmed the whole thing.
The rescue started at a depth of 27m and the water was cold, with limited visibility. We simulated an unconscious diver rescue.
The casualty was wearing a twin-set and stage, while the rescuer was wearing a rebreather and a stage. Obviously, a single-cylinder configuration is likely to involve slightly less effort.
Even before the start of the rescue, before the rescuer had even found the casualty, his heart rate was 140bpm. This is psychological stress combined with the normal effort of diving and cold water.
As the rescuer found the casualty and got hold of him, his heart rate was already 167bpm.
The rescuer carried out a very well-controlled lift, but at this point his heart rate was still at 167bpm, gradually increasing to just over 170 bpm.
It’s worth noting that the rescuer and the casualty were both instructors and were chosen for their typical build.
We deliberately chose typical divers rather than super-fit individuals so that we could get a realistic impression of the effort required by the average instructor.
As the rescuer approached the surface, his heart rate was 175bpm. This was primarily psychological stress, but bear in mind that the rescuer knew that this wasn’t a real rescue. It is likely that psychological stress would be even higher in a real rescue situation.