Peak force output

Whilst most studies measuring physiological change within the contact codes of football have examined what they termed maximal strength the present investigation examined peak force output using an IMTP measure. The term strength is used interchangeably with IMTP peak force output for ease of comparison with studies measuring strength through the performance of resistance training exercises requiring high load, low velocity force production (Cormie et al., 2008). Isometric testing has previously be found to be highly related to dynamic performance (Haff et al., 2005, Stone et al., 2004).

In this investigation increases in both IMTP peak and relIMTP peak were observed over the pre-season and competitive season. Whilst peak force output was

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significantly higher at the end of the season compared to the beginning of pre- season it is clear the largest increase in peak force output was observed during the pre-season period. Increases in 11.7% in IMTP peak were observed from the start of pre-season to end of the season. In the 8 week pre-season period (July to September) IMTP peak increased by 6.9% whereas the increase over the whole 33 week competitive season (September to April) was 4.5%. A very similar pattern was observed for relIMTP peak. It has been shown that frequency and volume are key variables in bringing about positive adaptations within maximal strength (Peterson, Rhea and Alvar, 2005). It is therefore likely that the greater increases in peak force output in the pre-season phase compared to the competitive season were due to the greater frequency and higher total volume of resistance training performed within this phase. It is possible that the greater increase in peak force output observed during the preseason period was in part due to the increase in FFM that occurred during the pre-season compared to the maintenance of FFM during the competitive season. Previous work has shown that a strong relationship exists between increases in muscle cross sectional area and increases in maximal strength (Cribb, Williams and Hayes, 2006, Blazevich, Gill and Shi, 2006). It has been suggested this is as a result of increases in the percentage of type II fibres within a muscle and/or changes in angle of pennation (Blazevich, Gill and Shi, 2006, Blazevich et al., 2007). Whilst this investigation does not provide any indication as to the specific changes in morphology that may be taking place as part of an increase in FFM, it does suggest an increase in FFM appears to contribute to an increase in maximal strength. Previous work looking at strength changes in rugby union players over a multi-season period has shown increases in lean mass are highly related to improvements in maximal strength (Appleby, Newton and Cormie, 2012). Practitioners should therefore consider including hypertrophy training in a periodized plan designed to bring about increases in maximal strength.

An additional reason for the greater increase in strength during the pre-season phase versus the competitive season is that the pre-season phase follows the off-season during which time a decline in some physical qualities often takes place (Nirmalendran and Ingle, 2010). Whilst subjects were given off-season training

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plans, the reduced volume, loading and unsupervised nature of training within this period means detraining is likely. Detraining in maximal strength has been previously reported in elite athletes during the off-season (Argus, 2012, Hakkinen and Komi, 1985). It is therefore possible that the increases in strength during the pre-season are largely a return to previous levels.

The finding of increases in strength following the pre-season phase is very much in keeping with the existing literature. Increases in maximal strength following the pre-season phase have been previously reported in both rugby league and rugby union (Harris et al., 1998, Argus et al., 2010). An increase in maximal strength of 11.3% was reported in professional rugby union players based in New Zealand (Argus et al., 2010). This is larger than the 6.9% improvement reported here. It is possible this difference could be due to the greater frequency of resistance training within the typical pre-season week for the New Zealand based players. Five resistance training sessions were performed each week by the New Zealand based players compared to four each week in the present study. Hoffman et al. (1990) have suggested that a weekly dosage of five sessions is likely to bring about greater performance improvements than three or four sessions. The difference between the magnitude of improvement in the two studies is also likely due to the different strength testing measures employed. It is possible that the more complex movement of the box squat 1RM test used by Argus et al. (2010) has more scope for technical improvement over a short period of time than the fixed position IMTP test employed in the present study. It is also possible that improvements in lifts such as the box squat can occur through improving force output around specific ‘sticking points’ (approximately 32°) within the motor pattern (Hales, Johnson and Johnson, 2009). The relevance of improvements in force output at such joint angles to rugby union performance is unclear. In contrast improvements in IMTP peak force occur at a specific knee angle (120-140°) known to have high relevance to sporting movements (Haff et al., 2005). It should also be considered that the box squat exercise used by Argus and colleagues (2010) was prescribed within training programmes as well as testing. This is likely to lead to greater familiarisation than would have been experienced with the IMTP in the present study given it was used exclusively as a testing modality. In addition to this it should be noted that Argus

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and colleagues (2010) did not publish reliability statistics for the subjects within their study.

The 4.5% improvement in strength reported in this study over the course of the competitive season is in keeping with much of the available literature. Previous studies in rugby league (3%), rugby union (4.8%) and American football (4%) have shown small increases or maintenance of lower body maximal strength over a competitive season (Argus et al., 2012, Baker, 2001, Fry and Kramer, 1987, Schneider et al., 1998). Several studies have in contrast reported decreases in lower and upper body maximal strength over the course of a competitive season in the contact codes of football (Dos Remedios et al., 1995, Legg and Burnham, 1999). The differences between testing methodologies employed by the studies will explain some of the variation in strength change reported. Variation between studies in terms of the volume and frequency of both resistance training and other types of training is however likely to be the key variable in determining the direction and magnitude of strength change (Peterson, Rhea and Alvar, 2006). Alongside the work of Argus et al. (2010) the findings reported here suggest it is possible for players to improve lower body maximal strength over the competitive season providing between 2 and 3 resistance training sessions are performed each week. This study builds on the work of Argus et al. (2010) as it shows it is possible for this strength increase to take place for a much longer period of time than the 13 weeks these authors examined. The present study also adds to that of Argus et al. (2010) by providing reliability for strength measures employed.

Whilst the IMTP test has not been previously used to evaluate changes in strength across a whole season it has been used to examine the strength characteristics of a variety of elite athletes including rugby league players (Stone et al., 2004, West et

al., 2011). The maximal strength values reported for subjects in this study are

approximately 20% higher than those reported for professional rugby league players by West and colleagues (2011). This suggests the subjects used here are of at least a similar training status.

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