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3 - Muscular Endurance and Strength
On today's battlefield, in addition
to cardiorespiratory fitness, soldiers need a high level of muscular endurance
and strength. In a single day they may carry injured comrades, move equipment,
lift heavy tank or artillery rounds, push stalled vehicles, or do many other strength-related
tasks. For example, based on computer-generated scenarios of an invasion of Western
Europe, artillerymen may have to load from 300 to 500, 155mm-howitzer rounds (95-lb
rounds) while moving from 6 to 10 times each day over 8 to 12 days. Infantrymen
may need to carry loads exceeding 100 pounds over great distances, while supporting
units will deploy and displace many times. Indeed, survival on the battlefield
may, in large part, depend on the muscular endurance and strength of the individual
soldier. Muscular
Fitness
Muscular fitness has two components: muscular strength and muscular
endurance.
Muscular strength is the greatest amount of force a muscle or muscle
group can exert in a single effort.
Muscular endurance is the ability of a
muscle or muscle group to do repeated contractions against a less-than-maximum
resistance for a given time.
Although muscular endurance and strength are
separate fitness components, they are closely related. Progressively working against
resistance will produce gains in both of these components.
Muscular
Contractions
Isometric, isotonic, and isokinetic muscular endurance and
strength are best produced by regularly doing each specific kind of contraction.
They are described here.
Isometric contraction produces contraction but no
movement, as when pushing against a wall. Force is produced with no change in
the angle of the joint.
Isotonic contraction causes a joint to move through
a range of motion against a constant resistance. Common examples are push-ups,
sit-ups, and the lifting of weights.
Isokinetic contraction causes the angle
at the joint to change at a constant rate, for example, at 180 degrees per second.
To achieve a constant speed of movement, the load or resistance must change at
different joint angles to counter the varying forces produced by the muscle(s)
at different angles. This requires the use of isokinetic machines. There are other
resistance-training machines which, while not precisely controlling the speed
of movement, affect it by varying the resistance throughout the range of motion.
Some of these devices are classified as pseudo-isokinetic and some as variable-resistance
machines.
Isotonic and isokinetic contractions have two specific phases -
the concentric or “positive” phase and the eccentric or “negative” phase. In the
concentric phase (shortening) the muscle contracts, while in the eccentric phase
(elongation) the muscle returns to its normal length. For example, on the upward
phase of the biceps curl, the biceps are shortening. This is a concentric (positive)
contraction. During the lowering phase of the curl the biceps are lengthening.
This is an eccentric (negative) contraction.
A muscle can control more weight
in the eccentric phase of contraction than it can lift concentrically. As a result,
the muscle may be able to handle more of an overload eccentrically. This greater
overload, in return, may produce greater strength gains. The nature of the eccentric
contraction, however, makes the muscle and connective tissue more susceptible
to damage, so there is more muscle soreness following eccentric work.
When
a muscle is overloaded, whether by isometric, isotonic, or isokinetic contractions,
it adapts by becoming stronger. Each type of contraction has advantages and disadvantages,
and each will result in strength gains if done properly.
The above descriptions
are more important to those who assess strength than to average people trying
to develop strength and endurance. Actually, a properly designed weight training
program with free weights or resistance machines will result in improvements in
all three of these categories. Principles
of Muscular Training
To have a good exercise program, the seven principles
of exercise, described in Chapter 1, must be applied to all muscular endurance
and strength training. These principles are overload, progression, specificity,
regularity, recovery, balance, and variety. OVERLOAD
The overload principle is the basis for all exercise training programs. For a
muscle to increase in strength, the workload to which it is subjected during exercise
must be increased beyond what it normally experiences. In other words, the muscle
must be overloaded. Muscles adapt to increased workloads by becoming larger and
stronger and by developing greater endurance.
To understand the principle
of overload, it is important to know the following strength-training terms:
• Full range of motion. To obtain optimal gains, the overload must be applied
thought the full range of motion. Exercise a joint and its associated muscles
through its complete range starting from the prestretched position (stretched
past the relaxed position) and ending in a fully contracted position. This is
crucial to strength development.
• Repetition. When an exercise has progressed
through one complete range of motion and back to the beginning, one repetition
has been completed.
• One-repetition maximum (1-RM). This is a repetition
performed against the greatest possible resistance (the maximum weight a person
can lift one time). A 10-RM is the maximum weight one can lift correctly 10 times.
Similarly, an 8-12 RM is that weight which allows a person to do from 8 to 12
correct repetitions. The intensity for muscular endurance and strength training
is often expressed as a percentage of the 1-RM.
• Set. This is a series of
repetitions done without rest.
• Muscle Failure. This is the inability of
a person to do another correct repetition in a set.
The minimum resistance
needed to obtain strength gains is 50 percent of the 1 -RM. However, to achieve
enough overload, programs are designed to require sets with 70 to 80 percent of
one’s 1 -RM. (For example, if a soldier’s 1 -RM is 200 pounds, multiply 200 pounds
by 70 percent [200 X 0.70 = 140 pounds] to get 70 percent of the 1 -RM.)
A
better and easier method is the repetition maximum (RM) method. The exerciser
finds and uses that weight which lets him do the correct number of repetitions.
For example, to develop both muscle endurance and strength, soldier should choose
a weight for each exercise which lets him do 8 to 12 repetitions to muscle failure.
(See Figure 3-1.) The weight should be heavy enough so that, after doing from
8 to 12 repetitions, he momentarily cannot correctly do another repetition. This
weight is the 8-12 RM for that exercise.
 MUSCULAR
ENDURANCE/STRENGTH DEVELOPMENT
To develop muscle strength, the weight
selected should be heavier and he RM will also be different. For example, the
soldier should find that weight for each exercise which lets him do 3 to 7 repetitions
correctly. This weight is the 3-7 RM for that exercise. Although the greatest
improvements seem to come from resistances of about 6-RM, an effective range is
a 3-7 RM. The weight should be heavy enough so that an eighth repetition would
be impossible because of muscle fatigue.
The weight should also not be too
heavy. If one cannot do at least three repetitions of an exercise, the resistance
is too great and should be reduced. Soldiers who are just beginning a resistance-training
program should not start with heavy weights. They should first build an adequate
foundation by training with an 8-12 RM or a 12+ RM.
To develop muscular endurance,
the soldier should choose a resistance that lets him do more than 12 repetitions
of a given exercise. This is his 12+ repetition maximum (12+ RM). With continued
training, the greater the number of repetitions per set, the greater will be the
improvement in muscle endurance and the smaller the gains in strength. For example,
when a soldier trains with a 25-RM weight, gains in muscular endurance will be
greater than when using a 15-RM weight, but the gain in strength will not be as
great. To optimize a soldier’s performance, his RM should be determined from an
analysis of the critical tasks of his mission. However, most soldiers will benefit
most from a resistance-training program with an 8-12 RM.
Whichever RM range
is selected, the soldier must always strive to overload his muscles. The key to
overloading a muscle is to make that muscle exercise harder than it normally does.
An overload may be achieved by any of the following methods:
• Increasing
the resistance.
• Increasing the number of repetitions per set.
• Increasing
the number of sets.
• Reducing the rest time between sets.
• Increasing
the speed of movement in the concentric phase. (Good form is more important than
the speed of movement.)
• Using any combination of the above. PROGRESSION
When an overload is applied to a muscle, it adapts by becoming stronger and/or
by improving its endurance. Usually significant increases in strength can be made
in three to four weeks of proper training depending on the individual. If the
workload is not progressively increased to keep pace with newly won strength,
there will be no further gains. When a soldier can correctly do the upper limit
of repetitions for the set without reaching muscle failure, it is usually time
to increase the resistance. For most soldiers, this upper limit should be 12 repetitions.
For example, if his plan is to do 12 repetitions in the bench press, the soldier
starts with a weight that causes muscle failure at between 8 and 12 repetitions
(8- 12 RM). He should continue with that weight until he can do 12 repetitions
correctly. He then should increase the weight by about 5 percent but no more than
10 percent. In a multi-set routine, if his goal is to do three sets of eight repetitions
of an exercise, he starts with a weight that causes muscle failure before he completes
the eighth repetition in one or more of the sets. He continues to work with that
weight until he can complete all eight repetitions in each set, then increases
the resistance by no more than 10 percent.
Continue to Specificity
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