SWEEPING CYCLE: FORCE, FREQUENCY, AND POWER

We know that sweeping causes frictional changes between the ice surface and curling stones, and this impacts stone trajectory. So, how should curling athletes sweep to maximise their impact on the ice surface and shot outcomes?

There are still disagreements, nuances, and developments regarding how to sweep most effectively. However, it can be agreed that there are 2 key variables that contribute towards effective sweeping:

Vertical force.

Sweeping frequency.

Sweeping with high vertical force and frequency causes greater frictional heating of the ice surface, and reduced stone-ice friction coefficients [Marmo et al., 2006]. With more effective sweeping comes greater potential to alter stone trajectory, and improved team shot making.

It is important to understand how these sweeping variables are measured, how they contribute towards sweeping efficacy, and how this understanding can be applied practically.

sweeping cycle

Vertical force and frequency dynamics vary throughout the sweeping motion. The sweeping cycle describes the sweeping motion in terms of these dynamics. Each sweeping cycle consists of 2 distinct phases:

Push phase: broom-head moves away from the athlete’s line of gravity.
Pull phase: broom-head moves back towards the athlete’s line of gravity.
1 sweeping cycle = 1 push phase + 1 pull phase

vertical force

Vertical force refers to the amount of weight that can be placed downwards, via the broom, and into the ice surface. It is dependant upon body mass, acceleration due to gravity, and acceleration from muscular contractions:

Force = Mass x Acceleration

Force is measured in newtons [N], and can be converted into kilograms [kg], as this is often easier for athletes to interpret.

Athletes utilise their body weight to maximise the vertical forces they are exerting. This can be seen with the ‘leaning’ technique that many sweepers now use.

Vertical forces are far higher during the push phase than the pull phase. These forces peak at the initiation of the push phase and are lowest at the initiation of the pull phase [Marmo et al., 2006].

sweeping frequency

Sweeping frequency refers to the number of sweeping cycles that are performed per second and is measured in hertz [Hz]:

Frequency = Sweeping cycles / Seconds

Broom-head velocity [m/s] and stroke length [m] are both variables which contribute towards sweeping frequency. Increasing broom-head velocity and limiting the length of sweeping strokes will lead to increased sweeping frequency.

Broom-head velocity fluctuates throughout the sweeping cycle. In each phase, velocity starts at 0 m/s, then accelerates to a maximum velocity, and then decelerates back to 0 m/s.

Using numerical models, it has been deemed that prioritising high sweeping frequency over high vertical force, will lead to greater increases in ice-temperature [Marmo et al., 2006]. This was attributed to the effect of overlapping brush strokes leading to improved ice heating. Curling athletes should consider ensuring they are not prioritising sweeping with high vertical force to the detriment of high sweeping frequency.

sweeping power

In a sporting context, power is defined as strength at speed. Power is a concept which incorporates both force and velocity, and has been researched extensively in a variety of sport and exercise fields [Baena-Raya et al., 2022]:

Power = Force x Velocity

The units of power are watts [W], and in sports, this is measured via the rate of force development of contracting muscles.

The relationship between force and velocity production abilities can be represented with a curve. As seen on the force-velocity curve, maximum force is produced when movement velocity = 0 m/s [isometric], and maximum velocity can only be produced at very low forces.

This helps in understanding why peak sweeping force occurs at the initiation of the push phase. The combined effect of broom-head velocity = 0 m/s, and the broom-head being at its closest point to an athlete’s line of gravity, explains why vertical forces are highest at this point.

This concept also somewhat supports the use of leaning, in that very high vertical forces can be produced, with reduced energy expenditure. This is due to the contractile velocity of the upper body muscles being close to 0 m/s. However, the forces exerted here will be limited by the athlete’s body weight. More research investigating the effectiveness of leaning on stone trajectory is needed to understand this further.

As the push phase develops towards its maximum velocity, there is a point where peak sweeping power is generated, with high vertical force and high broom-head velocity.

summary

There are 2 key component variables of effective sweeping:

Vertical force.
Sweeping frequency.

Both components are necessary to be able to maximise a sweeper’s impact on stone trajectory, through frictional ice heating.

The sweeping cycle consists of 2 phases:

Push phase: broom-head moves away from the athlete’s line of gravity.

Pull phase: broom-head moves back towards the athlete’s line of gravity.

1 sweeping cycle = 1 push phase + 1 pull phase

Force:

Measured in newtons [N] or kilograms [kg].
Force = Mass x Acceleration
Peak vertical force occurs at initiation of push phase.

Frequency:

Measured in hertz [Hz].
Frequency = Sweeping cycles / Seconds
Dependant upon sweeping velocity [m/s] and stroke length [m].

Sweeping power:

Power = Force x Velocity
Peak force and peak velocity cannot occur simultaneously.
Peak sweeping power occurs mid-push phase.

further thoughts

It is worth noting that much of the information included in this post comes from the research of Marmo et al. [2006]. This study was comprehensive, and its findings are still applied in practice today. However, the sport, sweeping devices, and techniques have developed since this time, potentially limiting the relevance of some findings today.

The research occurring currently, supported by World Curling [World Curling, 2023], will aid the curling community to understand how to best utilise force and frequency to sweep most effectively, within the sport currently. Continually updating and improving our understanding, through research, will only help strengthen the ability of curling athletes worldwide.

Further, research investigating power production in curling athletes would be very interesting. It would be expected that a greater ability to generate high rates of force development would translate to higher sweeping forces and frequencies. This could inform training and technique, to help athletes to sweep with greater effectiveness.

references

Baena-Raya, A., García-Mateo, P., García-Ramos, A., Rodríguez-Pérez, M.A. & Soriano-Maldonado, A. [2022] Delineating the potential of the vertical and horizontal force-velocity profile for optimizing sport performance: A systematic review, Journal of Sports Sciences, 40[3], 331-344. link

Marmo, B.A., Farrow, I.S., Buckingham, M.P. & Blackford, J.R. [2006] Frictional heat generated by sweeping in curling and its effect on ice friction, Proceedings of the Institution of Mechanical Engineers. Part L, Journal of materials, design and applications, 220[4], 189-197. link

World Curling [2023} World Curling Federation to support research on sweeping. Perth: Scotland. link