Ermanno Rampinini, Aldo Sassi, and Franco M. Impellizzeri

Introduction: Heart rate (HR) is used to monitor and to design aerobic training (1). Modern HR telemetric systems allow to collect training data during specific exercise with no discomfort. Using laboratory tests to determine the individual HR-VO2 relationship, it is also possible to better analyse the metabolic demands and the energy cost of the sport-specific exercises. Furthermore, even without the HR-VO2 relationship, HR itself could be considered indicative of the physiological effort (2) and it is possible to use it to define target exercise intensity zones (3). However, many coaches could not use HR monitors with all the athletes or during the whole soccer season. An alternative approach could be to determine the individual exercise intensities expressed as % of HRMAX of the typical exercises included in the training programme, using these measurements as reference data from which the physiological load imposed on the single athlete could be subsequently estimated. However, this strategy could be acceptable only if the reliability of HR during these exercise is high. Thus, the aim of this study was to determine the reliability of typical soccer specific exercises with and without the ball, commonly included in the training programme of a junior soccer team.
Materials and Methods: Fifteen soccer young players (mean ± SD: age 17.4 ± 0.5 yrs, weight 70.4 ± 5.2 kg, height 179.3 ± 4.1 cm, VO2MAX 53.3 ± 4.2 ml·kg-1·min-1), performed two times the same training session within one week. The players were part of the same team (Beretti Pro Patria Calcio, N=23). Training duration was 120 min and included warm up using the ball, 4vs4 (4x4 min), 4vs2 (2x4 min), 10vs10 (10 min) and two circuit tracks (A and B) without the ball (2x8 min) including direction changes, backward and lateral running, sprints, jumps, slalom and hills. During the whole training session HR was recorded every 5 s using an HR monitor (VantageNV and mod. S710, Polar Electro, Finland) but the athletes had no possibility to observe their HR.
Reliability was determined using Bland and Altman scatterplot (difference between the two HR training sessions expressed in % of HRMAX plotted against the measurements’ mean). Reference lines were determined as the mean difference ± 1.96 SD. Intra-class correlation coefficients (ICC) were also calculated.
Results: The exercise intensities expressed as % of HRMAX during the first training session were 76.6 ± 7.4 (warm up), 88.3 ± 3.0 (4vs4), 75.5 ± 4.6 (4vs2), 84.3 ± 3.5 (10vs10), 89.5 ± 2.5 (circuit A) and 89.2 ± 2.2 (circuit B). The exercise intensities expressed as % of HRMAX during the second training session were 73.1 ± 5.5 (warm up), 88.1 ± 4.5 (4vs4), 80.1 ± 6.2 (4vs2), 86.0 ± 5.6 (10vs10), 87.0 ± 2.7(circuit A) and 88.8 ± 2.1(circuit B).
The bias ± random error component (SD of the differences multiplied by 1.96) expressed as % of HRMAX for warm up with the ball was 3.5 ± 14.2, for 4vs4 was 0.3 ± 6.5, for 4vs2 was –4.5 ± 9.3, for 10vs10 was –1.7 ± 9.3, for CircuitA was 2.5 ± 2.4 and for CircuiB was 0.5 ± 2.5 (figure 1). ICC for warm up with the ball was 0.381, for 4vs4 was 0.624, for 4vs2 was 0.623, for 10vs10 was 0.488, for CircuitA was 0.888 and for CircuiB was 0.825.
Discussion: The results of this study showed a poor reliability of small group play HR (ICC from 0.381 to 0.624). On the other hand, the circuit track HR performed without the ball used in the present investigation and adopted by the coach of this team showed a good reliability (ICC 0.888 and 0.825), with HR differences within 0.1% and 5.0% of HRMAX during CircuitA and within –2% and 3% of HRMAX during CircuitB. These suggest that exercise intensity during running aerobic training is reliable and that could be performed without continuous HR monitoring during the training sessions. On the other hand, soccer specific exercise training using the ball need to be controlled with HR monitor. This could allow coaches to determine the actual individual cardiovascular load in order to optimise the following training sessions, or to control the compliance of the physiological stimuli imposed to players to the training previously programmed.

Journal of Sports Sciences, 22(6): p 558, 2004