DNF & CNF techniques comparison

Definitions

Dynamic apnea without fins (DNF) and Constant without fins (CNF) are two competitive disciplines recognized by AIDA. The nature of competition is defined as follows:

� 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 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 . Practically, this allows athletes of DNF to cover somewhat longer distances than CNF athletes. As a relevant case behind this argument, the CNF record

1 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 (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 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.

2 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos Energy consumption and buoyancy in DNF/CNF

As pre-dive 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 for each length in the pool” (Schagatay, 2010) as for example in Dave Mullin’s 218m world

3 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

4 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 , 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

5 DNF & CNF techniques comparison, (March 2011) Christos Papadopoulos must be noted that, even with perfect relaxation, the body’s basic functions () 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.,

6 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.

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

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

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

7 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 at www.research.usf.edu/diving/Scientific%20Diving%20Forms/powerpoint%20present ations/Diving%20Physics.ppt on March 13, 2011.

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

Shagatay, E., Kampen, von M., Emanuelson, S. & B. Holm (2000) Effects of Physical- 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 of Swimming. Medical Science Sports Exercise, 27(7): 1086 – 1089.

Stroemme, S.B., Kerem, D. & R. Elsner (1970) Diving Bradycardia during Rest and Exercise 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 during Breastroke: Analysis of 9th FINA World Swimming Championships. Fukoka.

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

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

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