Skadi

Tabbing Training

Men and women who undergo rigorous courses and selection procedures have the ability to carry heavy loads at speed over undulating and arduous terrain. As attrition rates are typically high, identifying the physiological underpinnings of successful loaded march/tabbing performance is key for aspiring individuals.

In predicting performance, the three physiological determinants of loaded march performance include measures of strength, body composition and endurance;

  1. Maximal oxygen uptake (VO2 max) is regarded as the ‘gold standard’ measure of maximal aerobic capacity was positively correlated with clean fatigue endurance performance (running) and loaded march performance. Individuals who have the ability to work at a given submaximal speed and the ability to maintain high percentages of their VO2 max without substantial increases in blood lactate concentration have been shown to perform best in endurance events (Saunders et al., 2004, Rayson et al., 2000).

Tabbing over arduous terrain, for long durations places a high amount of stress on the musculoskeletal system of the individual and has the potential to cause a variety of injuries ranging from lower back injuries, knee and foot pain, to stress fractures, and brachial plexus palsy. With low fitness levels associated with an increase in the risk of injury physical conditioning to increase fitness levels can provide a means of limiting loaded march injuries.

The aim of this training article therefore, is to determine evidence-based best practice for loaded march training and physical conditioning and provide practical guidelines to personnel on how to effectively condition the body for loaded march activities.

PTI Thompson: “Endurance comes to those who put in the time, the effort, and the heart. Seek out and train in the places where you feel most alive. Ultimately, if we aren’t in the arena and able to struggle for something worthwhile, we’ll never grow in resilience.”

Training for Loaded March Events

The Principle of Specificity

The principle of specificity refers to the need to conduct task specific physical conditioning, supporting the need for load marches to be included in a conditioning program designed to improve load carriage ability (Genaidy et al., 1989).

Although it may seem obvious to most, it is important to highlight the importance of specificity to improve load carriage performance. A study by Patterson et al. (2005) evaluated a specialized 12-week conditioning program for Australian trained personnel, which included circuit and resistance training, running, and load carriage marching. The study found that, while the individuals increased in strength and aerobic capacity following the program, completion time for a 15 km march (35 kg load) and an agility course (10 kg load) did not change significantly. The physical conditioning program was limited to just two load carriage sessions throughout the program (week 3 and 5). Furthermore, the duration of the longest load carriage march (30 minutes) was much shorter than the duration of the 15 km event (165 minutes). Thus, the findings raise the importance of frequency, intensity and volume required to elicit a training response for loaded marches.

Load Carriage Intensity, Frequency and Volume

Findings by Visser et al., (1995) found that load carriage intensity (load and speed) were a key factor in improving loaded march performance. The study compared a high intensity (load) and low volume (distance) training regime to one of a lower intensity (load) and higher volume (distance). Speed was kept constant at 5.5 km/h. Both training combinations were reviewed against the effects of training frequency (number of sessions per week). Their study found that, while all groups improved in strength, aerobic endurance, speed of march and progressive load march performance, the higher intensity (load), lower volume (distance) groups improved to a greater degree in the progressive load march test than the lower intensity, higher volume groups. Furthermore, the groups training with a higher frequency (once per week) improved to a greater extent than those training with a lower frequency (once per fortnight). These findings suggest that training improvement is best facilitated by intensity (load), followed by training frequency (sessions per week) and then by volume (distance).

In relation to middle distance marches (20km), Knapik et al. (1990) investigated the impact of a nine week conditioning program with the frequency of load carriage sessions ranging from none up to four sessions per month (0, 1, 2, 4 sessions per month with loads from 18 to 34 kg up to a distance of 16 km per session). The study found that the two groups training twice or more per month were 11 % faster over a 20 km distance (46 kg load). Interestingly, the study also found no significant differences between the groups that trained twice versus four times per month suggesting that a ‘law of diminishing returns’ exists, where fitness gains decrease with the amount of exposure (training frequency).

It is important to note that the differences in the findings of load carriage training frequency lie in the markedly different training programs, notably load carriage intensity (load) and load carriage volume (distance). Ultimately, as shown, for an individual to make significant gains in aerobic fitness and load carriage ability, the load carriage program needs to be specific and training must be at an intensity (load and speed) that is sufficient to stimulate adaptation.

Physical Conditioning: Concurrent Training

To support performance improvements in load carriage ability whilst in the gym, Kraemer et al. (2001, 2004) conducted a 12-week study, with groups training four times per week following resistance training (full body or upper body, power or hypertrophy orientated, and aerobic training (long distance running and sprint intervals), either in combination or in isolation. The conditioning programs that employed a combined training approach of both resistance training and aerobic training were associated with significant improvements in 3.2 km run (carrying 44.7 kg) completion time. Individuals following programs either in resistance or aerobic training in isolation failed to make any improvements in the loaded run times. This underpins the importance of upper body strength, which in turn improves posture maintenance, leads to an increase in energy efficiency and hence aids in improving load march performance.

Neuromuscular ability and aerobic fitness have been shown to improve load carriage ability (Frykman et al., 2000), with a combination of resistance training and aerobic training proven to be the most effective. Concurrent training involves training for more than one physiological response (such as strength and aerobic endurance) at the same time. As load increases (from 0 kg to 20 kg to 40 kg) individuals become less efficient, thus a higher absolute aerobic capacity is essential to performance, especially over varying gradients (4 km/h at inclines of 0, 3, 6, and 9 %) (Lyons et al, 2005).

Harman et al (2008), compared two physical conditioning programs, the first program followed a U.S. Army Standardised Physical Training regime (including loaded marches, stretching, calisthenics, sprints, shuttle runs, and medium-distance runs (12-18 mins runs) and the second a weight-based training program with an increased resistance training focus (including loaded marches, full body resistance, longer-distance, ability based, runs (20-30 min runs), sprinting, and agility training). Both groups were found to make similar, significant improvements in short duration load carriage abilities (400m with 18 kg load and 3.2 km with 32 kg load).

PTI Thompson: “Whether it’s 0600hrs, 2100hrs or both, we must do the work for its own sake, not for attention or for applause. And like the morning training routine, this mentality must be practised, expressed and nurtured by performing the task to the effort prescribed, no shortcuts, no distractions. This is where growth happens, this is how the mind teaches the body.”

The Principle of Recovery

Just as the training frequency, volume and intensity are important factors to consider in a load carriage training program, so too is the concept of recovery. The principle of recovery highlights the need for the systems of the body to have a sufficient recovery from the training stimulus to prevent overload and injury. Failure to provide recovery in the training program and to instead employ high volumes of vigorous weight bearing activities continuously has been shown to cause high injury rates among personnel. One means of providing recovery from a progressive training stimulus is to reduce the total volume (distance) of conditioning. This volume reduction strategy has been found to dramatically reduce injury rates during training, without negatively influencing fitness. Strategically placed recovery periods should be long enough to ensure that some musculoskeletal recovery takes place, yet short enough to limit detraining. Consequently, a structured and progressive conditioning program with built in recovery periods is recommended.

Finally, a point of caution, while load carriage conditioning may maximise an individual’s load carriage ability, there will still be a finite limit to the carrier’s physical ability. Body stature and body mass (height and weight) are two important factors that effect loaded march performance. Larger individuals might be able to carry heavier loads by virtue of their greater bone and muscle mass. Therefore, while a well-conditioned individual may be able to carry a heavier load than someone less well conditioned, there will still be a load threshold above which they will be overloaded.

Load Carriage Physical Training: Practical Implementation

F.I.T.T Principle

The F.I.T.T (frequency [how often], intensity [how hard], time [how long] and type of training) principle.

Frequency

Load march training should be conducted at a minimum of two times a month with loads those individuals are expected to carry on tasks (Knapik et al.,1993, 2004), with weekly sessions as opposed to fortnightly (Visser et al.,1995). A 10-day load carriage conditioning cycle (implemented in the Netherlands) may in fact be the optimal frequency. This frequency may however vary depending on training intensity (load, speed) and training volume (time or distance).

Intensity

To improve aerobic fitness, the loaded march training intensity (load, speed) needs to be sufficient enough to elicit a training response. Although higher intensity training has been shown to be the most effective in improving load carriage performance, the potential for injury following a long period of high intensity load carriage must be considered. Ultimately, the conditioning program needs to ensure that personnel are being conditioned to carry loads at the intensities required for tasks, whilst being cognisant of the fact that, no matter how much conditioning is undertaken, there is still a point beyond which the load carriage task will become too much for the carrier to physiologically withstand.

Time

The time (or distance) must be considered against both the intensity of the march and the outcome requirements. Just as short duration, high intensity sessions can be used to develop the ability to move rapidly for short durations, longer duration sessions are needed to develop the physical and mental stamina to endure long duration tasks (dismounted patrols, endurance marches, navigation exercises).

Type of Training

The principle of specificity identifies the need to undergo loaded marches to see performance improvements. However, the concept of concurrent training also suggests that other forms of physical conditioning may be useful to supplement the conditioning program, especially in injury prevention. Exercises which stimulate upper body strength and increase aerobic fitness, in particular, are the most effective for loaded marches, provided they do not become the focal point of the training and reduce time allocated to loaded march specific training.

Finally, the principle of recovery demands that the overall loaded march training program be structured and progressive, and include musculoskeletal recovery periods to help mitigate overuse injuries.

Loaded March Training Program: Implementation Guide

Optimal Load Carriage

For optimal performance and comfort during a march, carry weight as close as possible to the centre of mass of the body. A bergen places most of the load on the back and produces a forward inclination of the trunk and head that becomes greater as the load increases. The forward inclination keeps the load-plus-body centre of mass over the feet (the base of support), but this leads to repetitive contractions (and stress) of low back muscles. Just standing with a bergen increases postural sway (anterior-posterior, medial-lateral centre of pressure excursions) in a linear manner as the load increases. To improve comfort, internal frames and hip belts reduce shoulder stress. The shoulder straps of a bergen exert pressure on the skin. Shoulder pressure is considerably lower with a pack frame incorporating a wide hip belt, compared with a bergen or daysack without a hip belt. When a bergen with a hip belt are used for a load between 14 to 41 kg, the proportion of the load supported on the hips and lower back is 30% and the load on the shoulders is 70%, regardless of the load mass. There is a consistent anterior force exerted on the lower back that might increase stress in this area.

For bergens without frames or a hip belt, the majority of discomfort reported is most commonly in the neck and shoulder region. For a bergen with a hip belt, discomfort is located mainly in the midtrunk and upper legs. Overall, when a portion of the load is carried on the waist through use of a hip belt, there is less subjective discomfort than there is with shoulder load carriage. When walking uphill, individuals gave higher ratings for balance and ease of gait for bergens with hip belts that pivot in the sagittal plane.

Effects of Load Distribution  

The location of load in the bergen can affect energy expenditure, subjective comfort, and body mechanics. Higher energy costs have been associated with a load that was lower in the bergen and farther away from the body; lower energy costs were associated with loads placed higher in the bergen and closer to the body.

A more even distribution of loads using a rack system within the bergen resulted in considerably lower ratings of discomfort in the neck, shoulders, and lower back. Although both high- and low-load placements bring about forward body lean (knees, hips, shoulders, and head are farther forward), this effect is greater for low placements. This is because the lower load is closer to the ankles, which requires more forward body rotation to bring the bergen centre of mass over the feet.

Forward body rotation tends to bring the body’s centre of mass over the front half of the foot, which could increase the likelihood of foot strain and injury. Nonetheless, placement of the load high in the bergen tends to destabilise posture to a greater extent than lower placements, especially among tall men, as measured by the amount of body sway while standing with the load. Dynamic moments are about 40% greater with high-back placement, an affect attributed to the greater rotational inertia of the high load. A low or midback load placement might be preferable for stability on uneven terrain, particularly during unexpected stumbles, when high load placement can necessitate relatively high-muscle forces to maintain postural stability. The high-load placement might be best for even terrain because it keeps body posture with a load most similar to that without a load, and a high and more anterior load results in a lower energy cost than a low and more posterior load.

Effects of Rifle Carriage

Tabbing with a rifle restricts arm swing, adds weight, and moves the centre of mass more anteriorly. During rapid walking (5.4 km/h), a 4.5 kg rifle has minimal, but significant, effects on human gait. There are increases in forces produced at heel strike (ground impact forces, about 5%), forces to decelerate the body (maximum breaking forces, about 1%), and side-to-side forces (mediolateral impulse, about 12%). Many of these changes are less because of the mass of the rifle and are more associated with the restriction of arm movement, which increases the movement of the body centre of mass.

Physiological Factors Associated with Load Carriage

Recent studies confirm that body composition (fat-free mass), muscular strength (back and lower body strength), anaerobic capacity and aerobic capacity are positively correlated with loaded march performance changes. These studies highlight the components of physical fitness that should be trained to improve load carriage performance.

Female Load Carriage Considerations

Compared with men, women walk with shorter stride length and greater stride frequency. As loads increase, women’s stride length decreases, whereas men’s stride length shows no change. With increasing load, women also show a more pronounced linear increase in the time that both feet are on the ground (double support time) than do men. To bring the centre of the load mass over the feet (base of support), women tend to hyperextend their necks and bring their shoulders farther forward than do men, possibly to compensate for less upper body strength. Many of these differences between men and women persist even when differences in body size and composition are taken into account. When men and women were asked to complete a 10 km road march as quickly as possible carrying loads of 18 kg, 27 kg, and 36 kg, men were about 21% faster, regardless of load. Women commented more often than men that the pack straps were uncomfortable, that the belts fit poorly, and that the bergens were unstable.

An independent predictor of march time (when gender was included in the equation) was shoulder breadth. Because daysacks/bergen systems have been designed primarily based on the anthropometry of men, bergen systems designed considering the anthropometry of women can lessen the time gap between men and women. Studies suggest that the well-padded hip belt allows a better transfer of the load to the hips so that women can use the stronger muscles of the legs to carry the load. This might assist in improving female load carriage performance.

Medical Problems Associated with Load Carriage

Injuries associated with load carriage can adversely affect an individual’s mobility. Common tabbing related injuries are foot blisters, back problems, and metatarsalgia.

Foot Blisters

Foot discomfort can also be substantial, because of the development of hot spots and blisters. Foot blisters, the most common load-carriage-related injury, result from friction between the socks and skin, a product of point pressures exerted by the boot and the foot. Blisters can cause extreme discomfort, if they are not properly managed, especially in field conditions, they can progress to more serious problems, such as cellulitis or sepsis.

Heavy loads increase blister incidence by increasing pressure on the skin and causing more movement of the foot inside the boot through higher propulsive and breaking forces. Rifle carriage alone has minor effects on maximal breaking and propulsive forces. Other blister risk factors include tobacco use, low aerobic fitness, and ethnicity other than black.

Metatarsalgia

Metatarsalgia is a descriptive term for nonspecific, painful overuse injury of the foot. The usual symptom is localized tenderness on the sole of the foot under the second or third metatarsal head. Sutton (2018) reported a 20% incidence of metatarsalgia during a strenuous 7-month Airborne Ranger physical training program that included regular load carriage. One study reported a 3.3% incidence of metatarsalgia after a single, strenuous 20-km walk with soldiers carrying 45 kg. Metatarsalgia is usually associated with foot strain caused by rapid changes in the intensity of weight-bearing activity. Walking with heavy loads can be a predisposing factor for metatarsalgia, because this might cause the foot to rotate anteroposteriorly around the distal ends of the metatarsal bones for more prolonged periods of time, thus resulting in more mechanical stress in this area. Treatment includes rest, use of ice packs, elevation of the foot, and antiinflammatory medications. A metatarsal pad can be used. If symptoms persist, further evaluation for more serious problems (eg, fractures, tumors) is warranted.

Stress Fractures

Lower extremity stress fractures are common in untrained and trained personnel. Stress fractures are attributable to repetitive overloading of bones during activities, such as road marching. The most common areas of involvement are the lower extremities, especially the tibia, tarsals, and metatarsals. For metatarsal stress fractures, tenderness is generally localized on the dorsal side of the metatarsal shafts, which distinguishes the pain from metatarsalgia. Risk factors for stress fractures include the following: female gender, white ethnicity, older age, taller body stature, high foot arches, low aerobic fitness, prior physical inactivity, older running shoes, genu varus, and cigarette smoking.

Other factors that might increase risk include load carriage distance and walking style. Successful interventions in an effort to reduce the incidence of stress fractures include reduced running mileage, neoprene boot insoles, and calcium/vitamin D supplementation. A study demonstrated that reducing march speed, allowing individuals to march at their own step length (rather than marching in step), running and marching in more widely spaced formations and running on grass.

Summary

To summarise, this training article sought to provide evidence-based guidelines for improving loaded march performance. Appropriately designed physical training can improve an individuals’ load carriage capability. Tabbing with bergen loads over a period of weeks results in improvements in aerobic capacity (VO2 max) and decreases in the energy cost of carrying the load. Neither running nor resistance training alone will improve march speed, highlighting the importance that both aerobic capacity and muscle strength must be trained to improve loaded march capability. For more endurance based training articles see ‘Endurance Training: Tabbing for Time’.

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