Informational Constraints in Boxing: What sources of information do boxers use to coordinate their actions towards a target?

In combat sports learners need to become attuned to relevant properties of the environment that produce unique patterns of information flows (e.g., optical information from a punch bag or opponent's body). Such flow patterns can act as invariant information sources to constrain decision-making on the type of attack to be made (e.g., upper cut or jab). During training boxers learn to couple their movements to these critical information sources when selecting appropriate punches. Because of the time constraints on action, boxers need to narrow down the minimal information needed to select a stroke and to regulate their movements from the enormous amount available in the performance environment. In the sports sciences' literature there have been no previous attempts to study the perceptual variables that might act as informational constraints as boxers punch targets during practice. However, previous motor development and motor control research on interceptive actions point to some possible candidate variables. One candidate variable that contains relevant information for generating specific boxing actions could be based on information used to perceive a target's 'reachability'. Reachability has been shown to be perceived very early in infant development (Rochat, 1995; Rochat and Goubet, 1995), acting as a constraint on the tendency to reach in 4-5-month-old infants. Reachability depends on the distance to a target and on the relative propensity of an individual to lean forward (Yonas and Hartman, 1993). Theoretically, the capacity to perceive reachability from the information provided by a target is developed during infancy and could underpin decision-making in boxing since opponents cannot be contacted with a fist if he/she is not reachable. In other words, the decision to punch or not to punch could depend strongly on a 'perception of reachability' affordance (see Ulrich et al., 1990).

From this theoretical perspective, there were two main aims of the present study. First, we sought to identify some of the key informational constraints from the whole set that boxers might use to generate punching actions in a tactical manner. During training sessions, boxers explore and discover the most adaptive relations between the informational sources and their actions. Coaching literature from the martial arts in general suggests that one of the most important constraints regulating the punches of fighters is the perception of scaled distance to the opponent (e.g., Walker, 2003). From this text it is clear that expert pedagogists advise that most, but not all, punches should be completed from a distance that affords full extension of the hitting arm. In boxing, for example, optimizing the punching efficiency of jabs requires full arm extension, whereas hooks and uppercuts depend on coordinated phasing of elbow flexion and extension. Overextension of the arm should be avoided because it decreases the power of the punch and could cause over-balancing, providing an opportunity for an opponent's counter-attack (Walker, 2003). This reasoning led us to surmise that distance-to-target is a significant informational constraint on the decision making of fighters, and to clarify this issue we examined whether there was a relationship between specific distances and the type of punches selected by boxers.

Second, we believed that this type of informational constraint might interact with other constraints used by boxers to shape a kind of 'perceptual-motor landscape' of emergent actions based on their perceived efficiency of punches. We expected that the relations between intentionality and distance to target information would mould this perceptual-motor landscape in boxers as they selected the most efficient punches at specific locations. In this study we manipulated performer-target distances to understand effects of perceived striking efficiency in boxing, allowing us to plot the dynamic probability landscape of striking patterns that might emerge in boxers. During the task of punching a heavy bag, six classical types of boxing action patterns were under consideration: right jab, left jab, right hook, left hook, right uppercut and left uppercut. Our hypothesis was that the initial activation of a punching action, its probability of occurrence and its disappearance would all exhibit dependence on the distance to the target and on perceived striking efficiency by boxers.

METHODS

To achieve these empirical aims, 8 novice boxers, who had just completed a two-semester course of elementary boxing techniques, aged 21-23 years, were required to select appropriate punches to a black leather hanging heavy bag fixed to the wall with its bottom 95 cm from the floor. Two boxers reported weak left handedness and all other participants reported being right handed. Participants were not given prescriptive instructions on punches to be selected but were required to maximize the efficiency and the diversity of their punching actions. Figure 1A shows how a distance of one meter from the target was calibrated in 10 equal segments of 10 cms so that each performer could perform 60 punches at each distance to ensure efficient collision magnitude.

The choice of distance between the lower limbs in the parallel stance was left to the boxers. Also, there were no specific instructions on the movements of performers' feet except to maintain a constant distance from the target. At distance D = 0 (see Figure 1A), participants had to lean into the target (heavy bag) making the distance between their body and the target equal to 0. Participants were free to apply uppercut punches to any location on the target, including the bottom, middle or upper part of the heavy bag, depending on their perception of strike efficiency. Before starting the activity boxers were told to pay particular attention to the efficiency of the strikes produced and each boxer was questioned about their perceptions of punching efficiency for each shot selected after they had finished each sequence of activity. Perceived efficiency was scaled by participants on a 6-point (0-5) continuous scale with 0 reflecting absence of a stroke and 5 signifying a maximally efficient stroke. Modes of boxer-target co-ordination patterns were operationally defined as directions of upper limb movements with respect to the central visual line connecting the participant and the target facing him. This procedure allowed a notational strategy to be used in classifying shot frequency as a measure of decision-making. For example, right jabs have a dominant projection parallel to the central visual axis (z axis) and were numerically classified as 180 degrees. Left jabs, providing a mirror image of right jabs, were classified as -180 deg (see Figure 1B). Notation of hooks was considered to have projections along the sagittal (z) and horizontal (x) axes, with right hooks being classified as 90xz deg. and their mirror image left hooks as -90xz deg. (see also Figure 1C). Furthermore, upper cuts were recorded as projections on the sagittal (z) axis, with right and left uppercuts varying along the vertical (y) axis at 90yz deg. and -90yz deg. respectively (see Figure 1C).

In our analysis the following measures were recorded:

(i) scaled boxer - target distances D determined as a ratio between the physical distance of the participants from the target (X) and performers' arm length (L) i.e. D = X/L. Actually, the reachability condition can be formally expressed as R = X/( Leff + Llean) < 1, or as a scaled distance (ratio) between the objective physical target - participant distance X and the sum of the effective length of the arm (Leff) and the lean length (Llean). The effective length of the arm depends on the degree of flexion in the elbow joint. The larger the angle of flexion (as in hooks and uppercuts with respect to the jab strokes) the smaller is effective arm length. Llean = X - X1, where X1 is the distance measured from the target to the projection of the participant's active arm acromion process on the floor. If the forward lean leads the projection of the acromion to pass over the X position, which is a usual consequence of a forward lean, then a positive value of effective arm length will result. During participants' activity, due to the non-rigid instructional constraints Leff, Llean, and consequently reachability, R values were strongly fluctuating quantities and thus less suitable as stable distance measures.

(ii) the absolute probabilities of occurrence of action patterns i.e. relative frequencies p(k(D)) = k(D)/n, where k(D) is the number of occurrences of a certain type of punch at each scaled boxer - target distance (D) and n is the constant length of the sequence (n = 60); (iii) the mean group probabilities Pi of each of the three types of punches (jabs, hooks and uppercuts) at each scaled boxer - target distance (D): Pi(D) = 1 - Pj (D) + Pk(D), where Pi(D), Pj (D) and Pk (D) are the mean group probabilities of the three types of punches; (iv) mean group perceived punching efficiencies for each type of boxing shot (jab, hook and upper cut), at each scaled boxer - target distance: (E1,…,E3 (D)); (v) unpredictability of punching activity by the participants was assessed by the Shannon entropy measure: H(p(D)) = -Σi Pi(D)ln Pi(D); for (i =1,…,j; in our case j = 6, equal to the number of punching actions), i.e. as average information over all outcomes in the sequence; (vi) diversity was assessed by the symmetry measure S(p(D)) = 1 - (1/N) Σi |∆p(D)|i, for (i = 1,…,N), where N is the number of combinations of class 2 for a set of 6 elements (6 types of strokes), and | ∆p(D)|i is the absolute value of the differences between the probabilities of occurrence of each action pattern. In this study, for 6 possible types of strokes, there were N = 15 probability differences to calculate for each sequence per participant. (vii) efficiency ratio was calculated as E = Σi Ei (D) /Σi |∆E|i (D), for (i = 1…N), where N is the number of general types of actions (jabs, hooks and uppercuts) and the number of differences between the perceived punching efficiencies, making N=3; Ei (D) are the scaled distance (D) dependent mean group perceived punching efficiencies and |∆E|i(D) are the absolute values of the D dependent mean group perceived punching efficiency differences ( |∆E|1 = |Ejabs - Ehooks|; |∆E|2 = | Ejabs - Euppercuts|; |∆E|3 = | Ehooks - Euppercuts |). E measure increases if the sum of the perceived efficiencies increases and the sum of the perceived efficiency differences decreases. The group mean probability differences for the action modes were calculated as:

∆P1(D) = Pjabs(D) - Phooks(D); ∆P2(D) = Pjabs(D) - Puppercuts(D); ∆P3(D) = Phooks(D) - Puppercuts(D).

Keywords : Martial arts, boxing, affordances, decision-making, action selection

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