dnf cnf techniques comparison

1 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos

DNF & CNF techniques comparison

Definitions

Dynamic apnea without fins (DNF) and Constant weight without fins (CNF) are two

competitive disciplines recognized by AIDA. The nature of competition is defined as

follows:

� Dynamic apnea without fins (DNF): “The freediver swims in a horizontal

position under water to cover the greatest possible distance without any

propulsion aids (such as fins)” (Wikipedia, 2011).

� Constant weights apnea without fins (CNF): “the athlete (freediver)

attempts to dive to pre-specified depth following a guide line (rope) that he is

not allowed to actively use during the dive. Further, he is not allowed to drop

any diving weights during the dive and he also is not allowed to use any

propulsion aids” (Wikipedia, 2011).

Both techniques are enjoyable and very interesting even for amateur or beginning

divers. In those cases, technique or equipment is not really important. However, when

performed by professional or advanced divers, these two techniques have some very

important differences which one needs to consider.

Sources of differences

As both DNF and CNF techniques refer to breath-hold diving, it is important to note

the sources of differences in the way they are practiced:

� DNF is practiced in pools while CNF is practiced in the sea. This suggests

different water density and – potentially – different water temperature.

Practically, this allows athletes of DNF to cover somewhat longer distances

than CNF athletes. As a relevant case behind this argument, the CNF record


distance currently held by William Trubridge is 101m depth (202m total

distance) while the DNF distance record currently held by Dave Mullins is

218m (of course, this implies that the two athletes are of similar capacity but

we are confident that at such record-breaking levels they are).

� DNF refers to horizontal movement (gliding) while CNF refers to vertical

movement (diving). The major differences then in the two approaches are the

existence of alternating water pressure (CNF divers need to cope with pressure

while DNF divers do not), alternating temperature (CNF advanced or

professional divers need to cope with the cold associated with deep depths and

(less so but still important) light, as CNF divers are found swimming in much

“darker” waters (NOAA, 2011).

The main common element however between the two types of sports may be found in

the fact that there are no pre-set time limits within which the athlete is to cover any

distance (depth) – the limiting factor then becomes the athlete himself/herself, that is

his or her ability to combine as longer apnea periods as possible with the strength

required to move his or her body through the water to cover long distances.

It is evident then that the common element in both sports is the need for apnea for as

long as possible and the fact that work (body movement) needs to be produced while

in such condition (Schagatay, 2010). However, for DNF, the issue is to produce as

much work as possible (cover the longest possible distance) while for CNF a balance

between the work produced and the alternating depth at which this work needs to be

produced is the main objective. Therefore, in what follows we look at the most

important differences between the two sports in depth: energy consumption and

buoyancy issues. We also make a brief mention to other issues particular to CNF

(such as the temperature factor) and their influence in a third section. In section 3 we

elaborate on the efficiency of the kick and arm strokes and consider whether it would

be optimal to use any one of them independently (i.e., without combining them) while

in section 4 we summarize our results and conclude.


Energy consumption and buoyancy in DNF/CNF

As pre-dive oxygen storing has typically been maximized in both DNF and CNF

exercises through “packing”, a primary concern for both sports is the efficient

utilization of the athlete’s energy at the given oxygen levels. This “work economy”

(Schagatay, 2010) is influenced by the following factors:

� The efficiency of application of metabolic power used to create thrust and

propulsion for the athlete. Essentially, this refers to how efficiently the

athlete is able to transform the energy produced in his muscles into thrust

rather than to simple heat dissipated in the water but without helping him or

her propelling his or her body forward. In this respect, the athlete’s position in

the water as well as the athlete’s measurements (body, arms and legs size, size

of palms, etc.) are very important. More will be mentioned about this on

“pace” below.

� Appropriate weighing. Related also to the above is the issue of weighing, in

the sense that weights will need to assist or compensate the athlete’s body

weight for optimal diving. However, in the two techniques, weights are used

in a significantly different manner: in DNF, weights are used to “balance” the

athlete at a specific depth and hence allow him or her to apply his or her

energy for a forward thrust rather than for maintaining his depth. On the other

hand, in CNF, weights will be placed so as to “carry” the athlete at exactly the

desirable depth. Adding more than the optimum weight implies a difficult

time for the athlete to return to the surface, while less than optimum weight

suggests that the athlete will have to spend energy also while descending.

� Efficient turning. While this issue relates to DNF only (as it is practiced in a

pool and hence turning is of essence), efficient turning is very important as it

accounts for “a considerable portion of the propulsive force for each length in

the pool” (Schagatay, 2010) as for example in Dave Mullin’s 218m world


record DNF attempt (http://www.youtube.com/watch?v=PmAEjxkdxec). Of

course, turning is not an issue in CNF – even the change of direction at the

bottom has not really been considered (to the best of the author’s knowledge).

� Overall and apnea-specific fitness. Studies of overall fitness levels in breath-

hold divers have reported overall mixed results (Stroemme, Kerem & Elsner,

1970; Arnold, 1985), as it seems that overall fitness levels have conflicting

effects in DNF / CNF athletes: up to a point, it seems that the development of

swimming muscles contributes to increased power and, therefore, distance

covered. However, beyond that point, well-developed muscles contribute to a

higher oxygen consumption rate, even when no exercise is taking place,

shortening the time below water. As Schagatay (2010) reports “the

morphological characteristics of competitive apneists have not been studied,

but the impression is of greater variation in body composition compared to

athletes in other sports”, implying that free divers might need to focus on

building very specific muscles at the expense of others if they are to conserve

oxygen and maximize thrust during their dive.

To that respect, other studies confirming improvements in performance

through apnea-specific training seem to be in line with the above findings

(Shagatay, Kampen, Emanuelson & Holm, 2000).

� Equipment. This area is certainly one of difference between DNF / CNF as

DNF could (theoretically) be performed without a suit while CNF cannot (at

least in non-shallow depths) due to the (cold) temperature at such depth.

However, both activities today take place with special suits – which are

designed with a very different target in mind: for DNF, the purpose is purely

for the suit to allow for least resistance in water, while in CNF the purpose is

– beyond hydrodynamics – to insulate against the cold deep water

environment. According to certain studies (Starling et al., 1995), special


diving suits may increase gains in distance per stroke by 5% compared to

swimming trunks.

� Psychological issues. Although the precise mechanism by which

psychological training affects the ability of brain cells to become more

tolerant to hypoxia, it is commonly thought that appropriate training does

bring such results. Furthermore, appropriate psychological training assists

breath-hold divers to cope with aching muscles as well as respiratory

alertness. William Trubridge for example is quoted slowing his heart

(bradycardia) to the point where a monitor “discerns the atrial and

ventricular contractions as two separate beats” (Trubridge, 2007). In general,

it is thought that psychological relaxation lowers the base metabolic rate as

well as the need for oxygen, therefore leading towards significantly higher

performance.

� Swimming pace: pace is extremely important for both the DNF and CNF

athlete, but there are very different expectations in each technique. In DNF,

the objective is to swim at a constant “slow” pace (a “dance-like” pace as was

termed by some (Anonymous, 2011)) while at CNF divers need to “fight” the

buoyancy since, as they descend, air in the lungs is severely compressed and

buoyancy is reduced. Therefore, CNF divers will perform a number of hard

strokes at the start of the descend and the ascend and will allow their weights

to glide them upwards or downwards in-between. Also, connecting swimming

pace to the efficiency of delivering thrust through the swimming muscles

while minimizing the need for oxygen, we must note that energy and oxygen

conservation are by far more important than speed in this respect and,

therefore, the descending glide in CNF is not performed hands-first but rather

with hands in the sides (i.e., in a less hydrodynamic position but in one which

allows for a complete relaxation of the upper body). (See also William

Trubridge in http://www.youtube.com/watch?v=vF4PN8-2YSk). Finally, it


must be noted that, even with perfect relaxation, the body’s basic functions

(metabolism) continue operating, although at a much slower pace: therefore,

oxygen is consumed even if DNF/CNF divers do not perform any strokes (this

is the reason of course why perfectly still apneas are not indefinite). This

suggests that the athlete should not aim for a complete stop as any oxygen or

energy “expenditure” during this time is practically a waste. As shown also in

Trubridge’s video (http://www.youtube.com/watch?v=PmAEjxkdxec) he

starts the next stroke a fraction of a second before his body stops moving

through the water.

The arm and kick strokes: can they work independently?

Above, we have demonstrated the importance of energy efficiency – gaining

maximum thrust with minimal effort and with the greatest degree of relaxation – for

competitive DNF/CNF. With that in mind, a question that comes to mind is whether

this could be achieved by only arm or kick strokes, as suggested / questioned also in

several forums (DeeperBlue, 2011).

The fact is that the author has not been able to find a definite reference as to which

stroke might be the most efficient for DNF/CNF: relevant readings from surface

swimming (breaststroke style) suggest that arm and kick movements provide almost

the same thrust to the body, with arms having a slight edge (Maglischo, 2003; Takagi

et al., 2001). Feet on the other hand are typically able to deliver more work before the

athlete starts becoming tired – and fatigue is (as mentioned above) critical for this

particular sport.

With that in mind, it is quite understandable why top level athletes choose to perform

a mixed arms/legs routine with legs participating almost in a 2:1 ratio (see Mullin’s

video at http://www.youtube.com/watch?v=PmAEjxkdxec) over hands: the use of

both strokes allows fatigue to be distributed and by using them sequentially (i.e.,


without overlap) the athlete is able to rest the remaining parts, conserve energy and

maintain relaxation.

Summary and conclusions

In this study, we considered the common elements and the differences between two

competitive forms of breath-hold diving: dynamic apnea without fins (DNF) and

constant weights apnea without fins (CNF). From our research, we have found that

both forms require considerable fitness and specialization. However, to reach truly

exceptional levels, athletes will need to take into account a number of additional

parameters such as swimming technique, weighing, pacing and psychological

conditioning, amongst others. Most importantly, while it is expected that exceptional

athletes of each form will be very good at the other form, we would argue that

specialization in each form is essential at world record levels as human limits are

approached.

Finally, we have briefly reviewed the efficiency and power of the arm and kick

strokes and have found that while kick and arm strokes might provide sufficient

power to move breath-hold divers forward, their combination (or better,

synchronization) provides a more efficient use of the energy in the body as well as a

better tolerance of reduced oxygen levels through more relaxed work conditions –

efficient gliding becomes much more important than speed in this sport.

ReferencesAnonymous (2011) Accessed online at http://forums.deeperblue.com/constant-weight/73148-cnf-technique.html.

Arnold, R. W. (1985) Extremes in Human Breath-Hold, Facial ImmersionBradycardia. Undersea Biomed Research, 12:183-190.

DeeperBlue (2011) http://forums.deeperblue.com/freediving-training-techniques/.Accessed online on March 8.


Maglischo, E. W. (2003) Swimming Fastest. Human Kinetics. London, UK.

NOAA (2011). Diving Manual: The Physics of Diving. 4th ed. Accessed online atwww.research.usf.edu/diving/Scientific%20Diving%20Forms/powerpoint%20presentations/Diving%20Physics.ppt on March 13, 2011.

Shagatay, E. (2010) Predicting Performance in Competitive Apnea Diving. Part II:dynamic apnea. Diving and Hyperbaric Medicine. 40(1): 11-22.

Shagatay, E., Kampen, von M., Emanuelson, S. & B. Holm (2000) Effects ofPhysical- and Apnea Training on Apneic Time and Diving Response in Humans.European Journal of Applied Physiology, 82:161-169.

Starling, R. D., Costill, D.L., Trappe, T.A. Jozsi, A. C., Trappe, S. W. & B.H.Goodpaster (1995) Effect of Swimming Suit Design on the Energy Demands ofSwimming. Medical Science Sports Exercise, 27(7): 1086 – 1089.

Stroemme, S.B., Kerem, D. & R. Elsner (1970) Diving Bradycardia during Rest andExercise and its Relation to Physical Fitness. Journal of Applied Physiology, 28:614 –621.

Takagi, H., Sugimoto, S., Miyashita, M., Nomura, T., Wakayoshi, K., Okuno, K.,Ogita, F., Ikuta, Y. & B. Wilson (2001) Arm and Leg Coordination duringBreastroke: Analysis of 9th FINA World Swimming Championships. Fukoka.

Trubridge, W. (2007) CNF Technique. Accessed online athttp://forums.deeperblue.com/constant-weight/73148-cnf-technique.html. AccessedMarch 14, 2011.

Wikipedia (2011) http://en.wikipedia.org/wiki/Free-diving . Accessed March 13,2011.

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