Introduction

Heart rate (HR) is normally determined by the pacemaker activity of the sinoatrial (SA) node located in the posterior wall of the right atrium.1 HR can decrease or increase the intrinsic rate primarily by activation of the vagus or sympathetic nerve innervating the SA node.1 In individuals with high spinal cord injury (SCI), the autonomic innervation of the heart is impaired, resulting in lowered maximal HR (HRmax).2,3 Moreover, the increase in HR during exercise in these persons is mostly due to withdrawal of vagal parasympathetic stimulation.4 The parasympathetic stimulation may, as a consequence of the disturbed sympathetic innervation, give rise to autonomic dysreflexia in individuals with high SCI.4 In conjunction with factors such as reduced sympathetic nervous system, innervation and cardiovascular function, maximal exercise capacity is reduced when compared with able-bodied individuals.5

With the aim of analyzing the utility of the HR in high SCI players, some studies reported HR responses in laboratory environments along with oxygen consumption4 and rating of perceived exertion methods (RPE).6 In this sense, Valent et al4 reported that the HR–VO2 relationship appeared linear in only eight out of 18 high SCI participants, so that these authors question the use of HR monitors in this population when prescribing training intensity. Moreover, Lewis et al6 observed an absence of associations among HR, VO2 and RPE in motor complete SCI. However, all these studies have been realized in laboratory environments. Despite the results reported in this area, with the increasing professionalism of Paralympic sport, one of the main tools to measure the objective internal load are HR monitors in WB7–9 where some participants are high SCI players. Probably, if only the absolute HR values are taken into account, the difference between high SCI and non-SCI players would be high due to the reasons previously described. However, the proposal made by some authors10,11 to calculate the training load (TL) or match load (ML) based on the relative intensities of maximum HR could provide better information.

Therefore, the aim of this study was to describe the absolute and relative HR responses and match load of a complete high SCI player during a wheelchair basketball (WB) match. The second aim of the study was to calculate the differences in the absolute and relative HR responses and in the match load among this player and two non-SCI players in the same WB match.

Methods

Participants

Three Spanish first-division male WB players volunteered to participate in the study (Table 1). All of the participants were the only ones who played the whole official WB match. The participants were classified according to the Classification Committee of the International Wheelchair Basketball Federation (IWBF). This study was approved by the institutional Research Ethics Committee for Human Research (CEISH) of the University of the Basque Country (UPV/EHU). All participants provided written informed consent as outlined in the Declaration of Helsinki (2013).

Table 1 Wheelchair basketball player’s characteristics
Full size table

Procedures

To obtain individual peak HR (HRpeak), a 10 m Yo-Yo Intermittent Recovery Test Level 1 (YYIR1 10 m) as described by Iturricastillo et al11 was completed 1 week before the official match. This endurance test has been verified using WB players and has shown good reproducibility (ICC=0.83–0.94).12 The players were familiar with this test as it had been part of their usual fitness-assessment programme. During the test, HR was continuously monitored at 1 s intervals by telemetry (Polar Team Sport System, Polar Electro Oy, Kempele, Finland). One week after completing the YYIR1 10 m test, players performed in one official match. Moreover, during the match, the HR also was continuously monitored at 1 s intervals by telemetry. The total duration of the match was 92 min. The highest HRpeak value from the YYIR1 was at 10 m, or the match was used to determine the ML and HR zones ‘see below’.

Determination of match load (ML)

The match internal load of the player was evaluated by means of objective methods as previously used in WB.11 The objective methods included absolute (that is, HRmean, HRpeak) and relative HR (%HRmean and %HRpeak of the HRpeak), and the calculation of Edwards’ ML13 and Stagno’s (TRIMPMOD ML) ML14 summarized HR zones. The weighting factor is different for Edwards’ (90–100% HRpeak=5, 80–90% HRpeak=4, 70–80% HRpeak=3, 60–70% HRpeak=2, 50–60% HRpeak=1) and TRIMPMOD (93–100% HRpeak=5.16, 86–92% HRpeak=3.61, 79–85% HRpeak=2.54, 72–78% HRpeak=1.71, 65–71% HRpeak=1.25). Both methods provide the summation of the results to obtain the ML value (in arbitrary units, AU) and these AU were set for statistical analysis.

Determination of the percentage of time spent in each HR zone

Four HR zones were established, and the time and the percentage of time spent in each zone during the match were calculated. The HR zones were defined as low (<75% of HRpeak), moderate (75–85% of HRpeak), high (85–95% of HRpeak) and maximal (>95% of HRpeak), according to previously established criteria in basketball15,16 and in WB players.8

Statistical analysis

The total values are means±s.d. The delta value (∆%) between SCI-1 and non-SCI players was calculated using the formula: ∆%=((non-SCI-1 or non-SCI-2 − SCI-1)/SCI-1)×100. The coefficient of variation (CV): [(s.d./mean)×100] was used17 to assess the total HR responses values among the SCI and non-SCI players.

Results

The absolute HR responses of the YYIR1 10 m and the match load are presented in Table 2. The SCI player obtained lower absolute HRpeak responses in YYIR1 10 m than the non-SCI players (∆%=18.2–25.3%; CV=11.8–15.9%). The differences in the absolute HRpeak reached during the match between SCI and non-SCI players (∆%=13.2–22.6; CV=8.8–14.4%) were similar to those in YYIR1 10 m. Similarly, the differences also were observed in match absolute HRmean between SCI and non-SCI players (∆%=7.1–15.6%; CV=4.9–10.3%).

Table 2 The absolute heart rate (HR) responses during the 10 m Yo-Yo Intermittent Recovery Test Level 1 (YYIR1 10 m) and match
Full size table

The %HRmean and %HRpeak as well as the ML are presented in Table 3. As opposed to absolute HR values, relative HR values reported very similar responses among SCI and non-SCI values (∆%=−6.0 to −6.4%; CV=4.4 to 4.7%).

Table 3 The relative match heart rate (HR) responses and match load (ML)
Full size table

The time and the percentage of the total time spent in each HR zone are presented in Table 4. These relative HR values were similar in low, moderate and high zones between SCI-1 and non-SCI-1 players (∆%=−5.3 to 8.9%; CV=1.6 to 6.1%) and quite similar in the maximal zone (∆%=−13.3%; CV=10.7%). However, the differences between SCI-1 and non-SCI-2 were considerably different in the low, moderate and maximal intensities (∆%>−18.3%; CV>14.5%), while in the high intensity zone, the values were similar (∆%=−8.9%; CV=6.1%).

Table 4 The time and the percentage of the total time (%) spent in different heart rate (HR) zones during wheelchair basketball matches
Full size table

Discussion

Previous studies determined the questionable use of HR monitoring for exercise intensity quantification in persons with a high-level SCI,4,6 as these players could have an altered HR response. However, in the last years various studies have used HR methods to quantify physiological responses or the ML in WB matches,7,8 both for SCI and for non-SCI players. Identifying the absolute and relative HR responses in WB players could help coaches and physical trainers to understand how the level of injury may condition the physiological responses of the high SCI players. In this sense, the aim of this study was to describe the absolute and relative HR responses and the ML of a complete SCI player (T1–T2) during a WB match in order to compare with two non-SCI players.

The results of our study reported that, in absolute values the HRpeak and HRmean was lower in the SCI player than in the non-SCI players, both in YYIR1 and in the match. These results were in line with those of other.2,3 It is well determined that the impairment of the high SCI player could affect the HR responses due to an impairment in the autonomic innervation of the heart, preventing the high SCI players achieving the theoretical maximum or peak HR values,4 as it happened with the high SCI player. However, although the absolute HR could be different between high SCI and non-SCI players, in our study, the high SCI player could have obtained very similar relative HR (%HRmean and %HRpeak) and ML (Edwards’ ML and TRIMPMOD) values compared with non-SCI players in the official WB match. The impairment in the autonomic innervation of the heart could lead not to reach the peak HR, however, in this case, this impairment did not affect the relative HR values. This aspect shows that for the quantification of ML in WB might be necessary to relativize the data, as absolute HR values could distort the results.

Regarding the intensity zones, the results showed that the differences between SCI-1 and non-SCI-1 were distinct from the difference between SCI-1 and non-SCI-2 in the low, moderate and maximal intensities. The time and the percentage of the time spent in the high-intensity zone (85–95%) were similar in all the players. Therefore, when relativizing the HR, the differences in each intensity zone may not be due to the impairment but the game characteristics, the tactical and strategic aspects or the position in the court of the players.15

Conclusions

The authors are conscious that this study is a case report. Nevertheless, it could be that high SCI players even with a lowered maximum HR obtain very similar relative HR and ML values compared with non-SCI players in the same match. It is obvious that more studies should carry on in this line to verify if high SCI players have the same or similar relative HR responses than non-SCI players for the same training sessions, training tasks or matches in WB. However, although the level of spinal lesion determines the level of physiological system impairment, it seems that relative HR values may be very similar to non-SCI players. Thus, the same methods of quantifying relative HR responses and ML might be used for high SCI players and non-SCI players.