Biology of Sport, Vol. 28 No1, 2011 63 The effect of drop height and body mass on drop jump intensity Reprint request to: Hubert Makaruk Akademicka 2 21-500 Biala Podlaska, Poland e-mail: hubmak@poczta.onet.pl Accepted for publication 27.11.2010 INTRODUCTION In a number of sports, including athletics jumps [29], ski jumping [27], gymnastics as well as volleyball and basketball [7,30], performance depends, to a large extent, on the ability to resist large ground reaction forces during the landing (in the eccentric phase) [21]. For instance, in a 15-metre triple jump attempt the value of GRF in the step phase may be as high as 10 500 N, which is more than 15 times the body mass of a jumper [24]. In NBA players, during the landing after a lay- up jump shot the value may be 9 times the body mass [19]. Therefore, in these sports the application of exercises based on muscle activity in a stretch-shortening cycle (known as plyometric exercises) is well founded. These exercises increase an athlete’s tolerance for heavy loads that stretch muscles. As a result, while a muscle remains stretched in the same way, its stiffness increases. Thus it helps to gain greater force production and power output in the concentric phase [10,16,29]. Plyometric exercises that mainly involve the lower extremities are mostly performed as jumps. Drop jumps, which are basic plyometric exercises, consist in jumping off a box (usually 0.3-0.6 m high), making a two-legged landing with impact absorption (eccentric phase), followed by a powerful concentric movement. Like any physical exercises, they THE EFFECT OF DROP HEIGHT AND BODY MASS ON DROP JUMP INTENSITY AUTHORS: Makaruk H., Sacewicz T. The Josef Pilsudski University of Physical Education in Warsaw, Faculty of Physical Education and Sport in Biala Podlaska, Poland ABSTRACT: Given the nature of plyometric exercises (which overload muscles and joints), intensity control plays an important role in training. Therefore, the aim of this study was to determine the effect of drop height and mass changes on exercise intensity expressed through ground reaction forces (GRF) and the rate of eccentric force development (E-RFD). Nine elite male athletes representing 1 st league athletics clubs volunteered to serve as subjects for the study. They performed unloaded and loaded drop jumps from 0.2 m, 0.4 m and 0.6 m. As for loaded jumps, loads constituted 5% and 10% of body mass (BM). It was observed that with an increase in drop height, the values of ground reaction forces at the irst peak (the contact of toes with the ground; GRF 1 ) and at the second peak (the contact of heels with the ground; GRF 2 ) as well as the values of E-RFD 1 (measured from 0 to GRF 1 ) and E-RFD 2 (measured from 0 to GRF 2 ) increased signiicantly (P<0.01). An increase in BM from 5 to 10% led to a change in the values (P<0.05) of GRF 1 , GRF 2 and E-RFD 1 but only in the case of drop jumps from 0.6 m. However, the values of these parameters in loaded drop jumps with 10% BM were lower than those with 5% BM. The study results indicate that a change in drop height is a more effective way to manipulate the intensity of drop jumps than a change in body mass. KEY WORDS: stretch-shortening cycle, plyometric exercises, depth jumps, ground reaction forces, rate of force development may be deined by means of the volume expressed by work performed during jumps [31] or by the number of jumps [8] as well as by intensity, which is usually deined by such parameters as ground reaction forces (GRF) and the rate of force development (RFD) [15,18]. As far as drop jumps are concerned, these parameters are usually measured in the eccentric phase since their values are generally higher than in the concentric phase. Some researchers maintain that due to the nature of plyometric exercises (which overload muscles and joints), the skill to control exercise intensity plays a vital role in training [15,25]. However, in order to control exercise intensity skilfully it is necessary to know how it changes depending on ground type, jump technique, the type of jumps (one- or two-legged, vertical or horizontal, single or repeated) as well as drop height and additional loads. There are only a few scientiic [15] and methodological [9] studies in this area, so for the time being it is not possible to provide a systematic description of plyometric exercise intensity. In our opinion such a systematic description of intensity would facilitate planning and programming loads in plyometric training. Original Paper Biol. Sport 2011;28:63-67 - - - - - Electronic PDF security powered by www.IndexCopernicus.com