Rugby league is a contact sport that requires players to possess a range of physical qualities for success [1
]. Of these qualities, muscular strength and power might assist in the effective execution of several skills that determine performance or player selection. For example, upper-body strength and power have strong relationships (r
= 0.72 and 0.70, respectively) with tackling ability [2
], while upper- and lower-body strength and power are able to differentiate between playing standards in rugby league players [3
]. Upper-body power was only different between state and national standard rugby league players at higher external loads of 70 and 80 kg [5
], suggesting that power exerted against high external loads is a key discriminator of success in rugby league players. Baker and Newton [6
] also reported that upper- and lower-body strength and power characteristics were able to better distinguish between rugby league playing standards than other measures of acceleration, maximal speed, and agility.
Baker and Nance [7
] reported strong correlations between upper-body strength and power (r
= 0.89) and lower-body strength and power (r
= 0.81) in professional rugby league players. However, the relationship between strength and power might well be influenced by playing standard, with lower standard players presenting better associations (r
= 0.85) than national standard (r
= 0.58) players [3
]. This observation suggests that the training emphasis is likely to be different between players of different standards, with important implications for those designing resistance training programmes for the long-term development of rugby players. Regarding the contribution of barbell velocity to power output, Fernandes and colleagues [8
] reported that velocity was not related to bench press power in young resistance trained males. During the squat exercise, velocity was also moderately correlated (r
= 0.653) with power in these males [8
]. Interestingly, in stronger individuals, velocity appears to underpin adaptation to the lower-body power movements [9
]. A study in well-trained rugby league players that determines the contribution of both strength and velocity to power during upper- and lower-body resistance exercises would enable a closer examination of the interplay between these neuromuscular characteristics.
While recent studies have examined differences in physical qualities of senior, academy, and youth rugby league players [1
], measures of maximal strength, load–power, and load–velocity between rugby players of different training ages have not been provided before. In rugby union athletes, Hansen and colleagues [10
] noted that elite athletes (~26 years) produced higher power during the 40 kg jump squat exercise than their junior counterparts (~19 years) from the same team. However, the single load selected by Hansen et al. [10
] means that it is unknown if the differences in power exist at lower and higher loading conditions.
The primary aim of this study was to provide a detailed comparison of the load–velocity and load–power relationship among rugby league players of different playing standards within the same club. A secondary aim is to establish the contribution of strength and velocity to upper and lower body power in rugby league players.
This is the first study to provide a detailed analysis of the load–velocity and load–power relationships between rugby league players of different playing standards. These findings indicate that peak velocity and power are key descriptors of playing standard in rugby league players and thus provide a training progression for academy and scholarship players.
First grade players had a greater body mass than both academy and scholarship players, with academy values being higher than scholarship values. This is similar to previous reports of an increased body mass with playing standard [10
] and likely reflects differences in maturation [20
]. The lower body mass alongside higher sum of skinfolds in the academy players compared with their first grade counterparts would indicate a higher amount of fat mass and lower fat-free mass. Furthermore, the sum of skinfolds was not different for any other comparison. In support, Till and colleagues [22
] observed comparable skinfold values across 15 to 20 year old rugby league players. The fact that body mass increased with playing standard, but the sum of skinfolds did not for the first cf. scholarship and academy players compared with scholarship players suggests a greater fat-free mass in the higher playing standards. A greater fat-free mass in the higher playing standards might be attributable to the players’ resistance training exposure. For example, the scholarship and academy players’ exposure to resistance training took place recently (<2 years), while the first grade players had been regularly exposed to resistance training for longer (>7 years). Importantly, a lower skinfold thickness score is associated with enhanced skill related performance (e.g., sprinting, change of direction [23
]), but also supports the importance of a higher mass coupled with faster sprint speeds in senior player to optimise momentum into the collision [1
As expected, the first grade players had greater absolute and relative upper- and lower-body strength than academy and scholarship players. Scholarship players were also weaker, in both absolute and relative terms, than academy players for both exercises. Comparable differences in upper- [3
] and lower-body [6
] strength, between playing standards, have been reported previously. Like body mass, these strength differences might be explained by maturity and training age of the participants. A greater fat-free mass in senior players, indicated by a higher body mass and lower skinfold thickness, might also contribute to the higher force production in senior players [24
]. Together, these data reaffirm that upper- and lower-body maximum strength are key descriptors of playing standard between rugby league athletes.
Excluding the squat at 20 kg for all groups and 40 kg between first grade and academy players, peak velocity typically demonstrated moderate to large differences between groups. To our knowledge, no study has examined upper-body pushing velocity across different playing standards. As such, we report, for the first time, that bench press velocity is able to distinguish between rugby league players of different training ages. The fact that lower-body velocity is able to differentiate between playing standard is in support of a previous investigation in rugby union [10
], but contrasts reports in Australian rules players, where there were no differences observed between higher and lower standards [26
]. Notably, our study expands on previous work in that velocity was determined at a range of external loads rather than unloaded [26
] or single-loaded [10
] conditions. Rugby league players are expected to produce efforts against a range of loaded conditions, for example, sprinting and tackling. These differences in velocity might be explained by the greater strength with higher playing standards, and thus the absolute loadings accounting for a lower percentage of 1RM in the higher playing standards. Moreover, morphological (e.g., greater amount of type 2 fibres, pennation angle) and neurological (e.g., decreased antagonist coactivation, motor unit synchronisation) differences [6
] might provide a more mechanistic explanation of the differences observed in the current study. Practically, strength and conditioning coaches should aim to improve upper- and lower-body velocity at a range of external loads as players progress from lower to higher playing standards.
Peak power, similar to strength, reflected playing standard for all exercises and loads. That is, the first grade expressed higher peak powers than the academy and scholarship players, with academy values being greater than scholarship values. These data support previous observations in both upper- [3
] and lower-body power [4
]. Given that power is the product of force (strength) and velocity, these differences between playing standards are likely owing to the differences in strength and velocity between groups. Therefore, the higher power with playing standard can be explained by greater lean mass; maturation; training age; and, plausibly, morphological and neurological differences [6
]. Collectively, these data suggest that the enhancement of power, alongside other physical qualities [1
], is a pathway for progression in rugby league players.
For the bench press, strength was moderately correlated to optimal power in the scholarship players, but not first grade or academy players. The notion that the relationship between strength and power is decreased with playing standard has been observed previously [4
]. These data suggest that once players are relatively strong enough (i.e., a 1RM of >1.3 kg·bm−1
, as for the first grade and academy players), then other physical attributes must be focused upon. Indeed, the relationship between velocity and optimal power was moderate to strong for the first grade, academy, and scholarship players (r
= 0.514, 0.546, and 0.788, respectively). Only one study [8
] has generated comparable data, whereby velocity was strongly correlated to optimal power during the bench press in young resistance trained males. This suggests that high peak powers are achieved through greater velocity in better playing standards. During the squat exercise, only the academy players’ strength was correlated to optimal power. This reaffirms previous data [7
], but contrasts observations of no relationship between lower-body strength and power [21
]. The reason for the weak associations between lower-body strength and optimal power in the current study is unclear. Other factors, such as rate of force development [28
], might be of more importance in these populations and future studies should determine this empirically.