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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
2 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos
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.
3 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos
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
4 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos
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
5 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos
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
6 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos
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.,
7 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos
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.
8 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos
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.