Introduction The modern day tactical athlete has to be prepared to carry out their role in a range of climates and conditions, form hot and humid jungles to mountain warfare in freezing temperatures, from short duration patrols to long range reconnaissance. As part of their occupation, tactical athletes have to carry specific equipment in order to carry out their job and add to their safety whilst on operation. This equipment can consist of protective helmets, body armour, personal weapon and ammunition, surveillance equipment as well as food and water (Orr, 2012). These loads typically range between 20kg for light/short duration patrols, to over 50kg of equipment whilst out on long duration patrols (Laing & Billing, 2011) all of which has to be carried by the individual. As a result of tactical personnel carrying large loads for extended periods of time the stress upon the musculoskeletal system has led to an increase in injuries to the lower body and back resulting in an increase within non-deployable personnel (Cooper, 2014).
Impact of Load Carriage
Work by Smith et al., (2000) and Jones et al., (2000) reported musculoskeletal injury rates of 19.7% and 20% respectively, typically occurring during physical training. In addition to injury risks, heavier loads have been found to impact upon energy expenditure, mobility, lethality and task awareness (Orr et al., 2011). Increased load carriage has a profound impact upon energy expenditure which increased further when coupled with challenging terrain (Bobbert, 1960; Goldman & Lampietro, 1962; Haisman & Goldman, 1974).
(Graph taken from work by Knapik (2011): Physiological, Biomechanical and Medical Aspects of Soldier Load Carriage) In addition, through carrying heavier loads there is evidence to suggest there is also an impact upon the overall speed and mobility of the soldier with evidence to show they are 19% slower with a 14kg load and 44% slower with a 41 kg load between check points. They are also between 12-26% slower when crossing obstacles with the same respective loads (Pandorf et al., 2002; Park et al., 2010). Work conducted by Laing and Billing (2011) found that in addition to impacting speed over longer distances it also had a significant impact over short sprint distances of 5 and 30 metres. This impact upon a soldiers speed and mobility heightens their propensity for injury during contact situations as they will take longer to move between areas of cover.
The impact of system fatigue through carrying heavy loads has been associated with decreases in skill of marksmanship (Knapik et al., 1997; Knapik et al., 1991). Although the research findings are not congruent with other work by Knapik et al. (1993) as well as work by Patterson et al (2005) and Carbone et al (2014). Possible explanations for the disparity between study findings could be due to population group and testing methodology. In comparison to his studies in 1991 and 1997, Knapik et al (1993) chose a population group drawn from Special Forces as opposed to regular infantry to cover the same 20km. In addition, they were provided with a 10 minute rest period before beginning the marksmanship task as opposed to 5 minutes used in the other two studies. The associated high levels of fitness that is possessed by Special Forces personnel could be a contributing factor to their ability to recover over a short time frame or that the rest period used in the 1991 and 1997 studies were just too short. This longer rest period is in agreement with work by Patterson et al (2005) who implemented a 30 minute rest period between finishing a 15km march and conducting their marksmanship test, finding no negative effect upon shooting performance. The study by Carbone et al (2014) differs in that it consisted of tactical police officers who had to sprint through a 25m course wearing body armour before engaging a fixed target. Unlike the previous studies which had a longer duration aerobic element, Carbone et al (2014) work was more anaerobic in nature and participants wore body armour as opposed to a loaded Bergen. This short duration coupled with a lighter load that is more evenly distributed over the body could explain the lack of decline in shooting accuracy. One final factor to be considered is that the firearm consisted of using a pistol side arm whereas the previous studies were all conducted using a rifle. This could contribute to the variance in results as a pistol is possibly easier to control than a rifle when fatigued, in addition to taking on a more squared off posture when using a pistol. Reducing Injury risk and increasing performance
Table 1: Incident of load carriage injury (Orr, Johnston, Coyle & Pope, 2014)
Graph 1: Load Carriage injury by body site (Orr, Johnston, Coyle & Pope, 2014)
Graph 2: Nature of injury (Orr, Johnston, Coyle & Pope, 2014)
The above table and graphs show the common injury sites to be the lower back and leg with a high re-occurrence of injury. This risk of re-injury ties in with previous research showing that the greatest indicator of injury is previous injuries (Worrell et al., 2006; Brandsson et al., 2001). There is a body of research that investigates the application of physical training in order to minimise injury risk and enhance performance. The research has looked at the use of aerobic and strength training both separately and combined and the subsequent impact on load carrying performance, along with studies in to increases of load carrying frequency on performance (Hamren et al., 1998; Patterson et al., 2005; Rudzki, 1989; Kraemer & Szivak, 2012). From the research there are several studies that agree with the principle of specific adaptations to imposed demands, in order to improve at load carrying tasks individuals have to engage with it as part of their training (Harmen et al., 1998; Visser et al., 1995; Knapik et al., 1990). The training effect from regular frequency of walking with load can lead to increase aerobic fitness and a decrease in energy expenditure (Rudzki, 1989; Knapik et al., 2004). Interestingly, in there 2005 study, Patterson and colleagues found that improving soldier’s strength and aerobic capacity following a 12 week program there was no significant improvement upon a timed 15km march while wearing a 35kg pack.
Possible reasons for this can be attributed to this are the frequency of the weighted marches used as part of the training program with soldiers only engaging within two sessions based early on in weeks 3 and 5. Additionally, the longest training march consisted of 30 minutes, significantly shorter than the 165 minutes duration of the 15km test. Studies that focused on loaded walking frequency found more positive results when individuals engaged within 2-4 sessions per month (Knapik et al., 1990; Harmen et al., 1998). Harmen et al (1998) found that female recruits who engaged within 75 minutes of loaded walking with loads between 11 and 34kg increased their average speed over a 2 mile course from 3.5 to 5.5mph over a 26 week period. Although positive, the results of Harmen et al., (1998) study need to be interpreted with some caution due to the short duration of the testing distance it cannot be assumed that the shorter 75 minute training duration would have as significant an impact on longer loaded marches, such as the 165min march used within Patterson et al., (2005) study. This principle of specificity is highlighted in work by Kraemer et al. (2001, 2004). Over the course of 12 weeks (Kraemer et al., 2004) and a longer 24 week study (Kraemer et al., 2001) had males and females separated in to three groups ; consisting of resistance only, aerobic only and a concurrent training group who engaged within both resistance and aerobic training. All groups trained three times per week engaging in various resistance protocols (full body or upper body, power orientated or hypertrophy orientated), aerobic based training (long distance running and sprint intervals). The group that engaged with concurrent resistance and aerobic training achieved significant improvements within their 3.2km run times whilst carrying a 44.7kg load. Intriguingly, in both studies, the participants who engaged within a single training modality, either resistance or aerobic only, failed to make any significant improvements within their loaded run time performance.
Conclusion and recommendations It is clearly evident from the research that in order to increase performance within walking with heavy loads it is best to have a complete program that focuses upon developing general physical qualities such as strength and aerobic capacity (Kraemer et., 2001; Kraemer et al., 2004; Kraemer et al., 2012; Harmen et al., 1998), in addition to, specific training involving walking under load (Rudzki, 1989; Knapik et al., 2004). General resistance training should look to develop maximal strength through compound movements in order to develop bone density and increase tissue tolerance to high stress loads (Kraemer & Szivak, 2012). As with traditional training modalities work by Drain, Orr, Attwells and Billing (2012) suggest that loaded walking should be progressive in nature. One such possibility they suggest is through the application of prescribed load as a percentage of the individual’s bodyweight. Although this may not be near operational load limits it provides an initial starting point that can be steadily progressed towards an end point load that could be considered operationally relevant. In addition, this modality could be used as part of a rehabilitation program to reintroduce loaded walking to previously injured individuals.
Reference
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