The overall landscape of training methods and individuals who participate in recreational exercise is vast and varied.Who are these individuals, and what do they do? Let’s use “David” as an example. This fictional recreational-exercise client is an avid basketball player for an all-men’s league.
His team plays twice a week, but David still wants to stay conditioned and maintain his strength. Therefore, he runs on the treadmill for 30 minutes 1–2 days a week and performs a strength training regimen 2–3 times a week. You may have clients whose needs are similar to David’s—recreational exercisers and athletes who are not at the level of Olympic power lifters or elite marathon runners. Nevertheless, these clients want to remain active and participate in sports such as cycling,
running, basketball, swimming and weightlifting—either for fun or for competitive reasons. During training periods, recreational exercisers or athletes usually perform both endurance and strength training, a strategy referred to as concurrent training (Leveritt et al.1999). The principle underlying this strategy is that people like David can attain benefits from practicing endurance and strength training either in the same workout or within the same time period.

The training for a high-strength,
high-power activity such
as weightlifting or for a high-endurance,
aerobic power event such as marathon running may seem uncomplicated when you are designing a single training program (Nader 2006). Traditionally, low-intensity endurance activities require light-resistance,
high-repetition training.
On the other hand, high-intensity,
short-duration activities benefit from heavy-resistance,
low-repetition training (Hickson 1980). Designing programs for sports and activities that demand a combination of strength and endurance training can be more complicated (Nader 2006). In exploring the concept of concurrent training, this article first reviews the adaptations involved in strength and endurance exercise;
then looks at the relevant research, both negative and positive;
and concludes with practical ideas on how to apply concurrent-training concepts to program design for recreational
exercisers and athletes.

General Adaptations of Strength Training

Most individuals train with weights in order to change their body composition and to increase the strength or size of their muscles. Clients who perform high-intensity,
short-duration activities employ heavy-resistance,
low-repetition training using various
strength training modalities. The act of strength training itself requires energy from our two anaerobic energy systems: ATP-CP
and glycolysis. The ATP-CP energy system is used during short-duration,
high-intensity activities with long rest periods,
whereas the glycolytic energy system is relied on during longer, less intense exercise bouts with shorter rest periods. Intermittent recovery during rest periods is extremely important for maintaining sufficient intensities to yield maximum gains.

The most important adaptation of resistance training is muscular hypertrophy and,
thus, increases in strength (National Strength and Conditioning Association [NSCA] 2000). Strength gains are first made within 6–8 weeks as several neuromuscular factors are enhanced: neural activation of the muscle improves; motor unit recruitment and synchronization become more efficient;
and there is increased excitability of the alpha motor neurons.
Later strength gains are seen with subsequent muscle fiber enlargement (NSCA 2000; Millett et al. 2002). Additionally, strength acquired through resistance training has been shown to enhance speed and anaerobic capacity (NSCA 2000).

Strength training has an immense effect on other performance variables as well.
It can increase muscle endurance for high power output and maximal rate of force production, and it can improve a client’s vertical jump ability. In addition to hypertrophic effects,
strength training elicits other muscular adaptations,
such as decreases in capillary and mitochondrial density; increases in the amount of fast heavy-chain myosin;
and conversion of
type II muscle fiber subtypes to almost all type IIa muscle fibers (NSCA 2000).

Other physiological variables affected by strength training include enzymatic activity, metabolic energy stores, connective tissue and body composition. Enzymatic activity within the muscle increases for creatine kinase,
myokinase and phosphofructokinase.
Interestingly, these enzymes are important regulators of the two anaerobic energy systems mentioned previously. Strength training also raises the stores of ATP, creatine phosphate, glycogen and possibly triglycerides in muscle.
Other proposed benefits include improvements in ligament and tendon strength, collagen content and bone density. Resistance training also decreases body fat percentage and increases fat free body mass (
NSCA 2000).

Endurance and strength training often present opposing adaptations (
Chtara et al. 2005; Glowacki et al. 2004). The main adaptation of
endurance training is an increase in the muscle’s aerobic capacity. This allows an individual to perform a given exercise intensity for a prolonged period of
time and at a higher maximal aerobic power, or VO2max, than was possible prior to training. Examples of endurance training include running, swimming, cycling and recreational sports such as basketball. According to the NSCA, endurance training increases cardiovascular power, but it does not increase muscular strength or size (NSCA 2000).

Endurance training may increase aerobic power and muscle endurance during low-power-output activities,
but it has no effect on muscle strength in consort with maximal rate of
force production, vertical jump, anaerobic power or sprint speed. Again, endurance training does not affect muscle size or fast heavy-chain myosin,
but it does increase capillary and mitochondrial density in the muscle (
NSCA 2000).

Like strength training, endurance training has positive effects on creatine kinase and myokinase activity and raises the levels of stored ATP, creatine phosphate, glycogen and intramuscular triglycerides. Ligament and tendon strength improves, and—provided the activity is weight-bearing—bone density increases, in proportion to the load. Endurance training can also decrease body fat percentage (NSCA 2000).

Negative Research on Concurrent Training

The rationale behind concurrent training is that clients will see
simultaneous gains in endurance and strength (Leveritt et al.
2003). However, not everyone agrees that this can happen. The
NSCA’s position on concurrent training is that (1) resistance or
strength training has no impact on aerobic power and (2) aerobic
endurance training can compromise the benefits of resistance
training (NSCA 2000).

Research has shown that simultaneous benefits in strength
and endurance from concurrent training may not be possible. In
fact, some studies, but not all, have shown that concurrent training
may hinder training adaptations for both muscular
endurance and strength (Glowacki et al. 2004; Hickson 1980;
Leveritt et al. 1999; Nader 2006). Hickson (1980) determined that
little or no benefit was possible for endurance athletes performing
concurrent training and, in addition, concurrent training had
detrimental effects for strength training athletes. Glowacki and
others (2004) showed a significant increase in VO2peak with
endurance training, but not with strength or concurrent training,
demonstrating that resistance training might have a negative
effect on endurance training. In this same study, the authors
suggested that strength training could be superior to concurrent
training when muscle power was the ultimate goal and that concurrent
training might interfere with improvements in cardiovascular
capacity (Glowacki et al. 2004).

Lactate threshold can be a marker of cardiovascular
endurance, and researchers have studied threshold changes in
relation to concurrent training. In trained endurance athletes,
strength training may not have a negative effect on lactate threshold,
but it is also unlikely to supply the necessary stimulus to have
a positive effect (Jung 2003; Paavolainen et al. 1999). Unfit
individuals, on the other hand, may actually see a benefit from
strength training in addition to endurance training.

Other negative drawbacks of introducing strength training to
an endurance regimen, besides the ineffectiveness in enhancing
either strength or endurance (according to some studies), are
body mass gains and possible injury (Jung 2003).

Concurrent Training and Decreased Performance

Why might concurrent training hinder strength and endurance
development? Potential mechanisms include acute fatigue, neuromuscular
adaptations, overtraining, skeletal muscle factors and
changes in the anabolic-catabolic hormone balance.

Acute fatigue is a possibility when performing endurance and
strength training on the same day. The first bout of activity,
whether it is endurance or strength training, can cause exhaustion
that may carry over and compromise gains in the second
bout of activity.Over time this cycle can lead to either no training
adaptations or very minimal positive results compared with
no first bout of activity (Chtara et al. 2005; Leveritt et al. 1999;
Leveritt et al. 2003). The recovery time between bouts can also
be a limiting factor when trying to obtain advantageous strength
and endurance adaptations (Leveritt et al. 1999).

The neuromuscular adaptations that occur in fast- and slow-twitch
motor units during endurance training may affect
resistance training gains and hinder strength development.
Enhancing the metabolic and contractile properties of slow-twitch
motor units through endurance activity negatively
impacts the function and recruitment of fast-twitch motor units,
thereby affecting overall strength and power output development
(Dudley & Fleck 1987). Endurance training may also reduce
power, owing to the neuromuscular system’s decreased ability to
generate force. Therefore, concurrent training may hinder
strength development by impairing the neuromuscular system’s
ability to recruit motor units efficiently (Dudley & Fleck 1987;
Leveritt et al. 1999; Leveritt et al. 2003).

Overtraining refers to any physiological or psychological factor
that leads to a decrease or no alteration in performance even
when there is adequate training stimulus (Hickson 1980). Fatigue
caused by overtraining can result from excessive training frequency,
volume or intensity and also from lack of proper rest and
recovery (NSCA 2000). Some researchers have suggested that
individuals who perform concurrent endurance and strength
training are more susceptible to overtraining than those who do
strength or endurance training alone (Bell et al. 1991; Leveritt et
al. 1999; Leveritt et al. 2003).

The body adapts to both endurance and strength training, but
a conflict in the skeletal muscle can occur with concurrent training.
Skeletal muscle will attempt to adapt to both training
extremes, which can be hard or even impossible (Leveritt et al.
1999). The difficulty occurs because the muscle cannot positively
adapt to two different demands from two different energy pathways
during the same training session (Chtara et al. 2005).
Research has illustrated that when endurance training is added
to strength training, limitations in muscle hypertrophy can interfere
with strength gains (Bell et al. 2000; Leveritt et al. 1999).

Concurrent training can alter endocrine responses by causing
changes in the anabolic-catabolic hormone balance. Strength
training supports anabolic processes, such as muscle hypertrophy,
whereas endurance training is more catabolic in nature, thus
hindering strength development (Leveritt et al. 1999). When the
body functions in a catabolic state, cortisol levels increase above
normal levels. With little or no change in anabolic hormone concentration
(testosterone, growth hormone) in this catabolic state,
overtraining is likely with concurrent training (Bell et al. 1991;
Bell et al. 2000).

Positive Research on Concurrent Training

While some research has noted negative consequences to concurrent training, other findings are more positive. According to
the NSCA, including strength training in an endurance training
program can improve the ability of the heart, lungs and circulatory
system to perform under conditions of high pressure
and force production (NSCA 2000). Hickson (1980) found that
strength training had little or no effect on endurance performance;
however, strength training did increase the time to
exhaustion in high-intensity cycling and running. Therefore,
Hickson concluded, strength training might be beneficial in
endurance events where a “sprint finish” was needed (e.g., at the
end of a running or cycling race).

To be advantageous in an endurance regimen, strength training
must affect certain variables responsible for running performance,
such as VO2max, lactate threshold and running economy (Jung
2003). Research suggests that anaerobic factors and neuromuscular
characteristics (the interaction between the nervous and muscular
systems) may also play a role in endurance performance.

Chtara and others (2005) demonstrated positive results when
combining endurance and strength exercises. They found that
concurrent training produced improvements in aerobic capacity
and endurance performance, especially when endurance
training preceded strength training in the same session (Chtara
et al. 2005). The increases in strength that McCarthy and others
(1995) observed during concurrent training were similar to the
gains they observed when strength training was performed separately.
These researchers also demonstrated that combination
strength and endurance training did not hinder increases in aerobic
fitness that would also be produced by endurance training
alone. They concluded that the increases in aerobic capacity
might be related to the increase in fat-free mass and the muscle
hypertrophy elicited by strength training and potentially to the
short rest periods and high intensity of the strength program.

Paavolainen and colleagues (1999) determined that a combination
of explosive strength training and endurance training significantly
improved 5K running performance in endurance
athletes. The progressions were made without changes in
VO2max, suggesting increases in muscle power and running
economy. Strength training may decrease ground contact time
by improving the stretch-shortening cycle, thus enhancing running
economy (Paavolainen et al. 1999). In a different study, researchers
observed increases in running economy following
concurrent strength and endurance training in well-trained
triathletes (Millett et al. 2002).However, these improvements did
not occur with endurance training alone, possibly because of a
decrease in muscle power and negative changes in neuromuscular

Muscle stiffness, degree of neural input to the muscles,
motor unit synchronization and motor unit recruitment can
all affect running economy (Jung 2003; Paavolainen et al. 1999).
Millett and others (2002) concluded that the addition of heavy
weight training to an endurance training program did not affect
VO2 kinetics in well-trained triathletes. The researchers found
that a greater number of fast-twitch motor units were recruited
to compensate for the decrease in power output caused by the fatigued muscle. By improving muscular power and neuromuscular
characteristics through strength training, an individual can
positively affect his endurance through improved running economy
(Jung 2003).

When training to improve endurance in recreational athletes,
it is important to emphasize maximal force in a strength program
(Hoff, Gran & Helgerud 2002). Strength training may not increase
VO2max, but it can still be beneficial to an endurance athlete.
Improvements in endurance training can occur with some
type of strength training through benefits garnered from neuromuscular
characteristics, running economy or anaerobic capacity
(Jung 2003).

Concurrent Training: Practical Suggestions

There is still a lot of controversy associated with concurrent endurance
and strength training. This may be due to the variations
in regimens and experimental designs (Bell et al. 1991). However,
by considering factors such as modality and duration, session sequencing,
timing, volume, intensity and training frequency, as
well as the training status of the individual client, trainers can develop
an effective model for concurrent training (Chtara et al.
2005; Glowacki et al. 2004; McCarthy et al. 1995).
In order to see positive concurrent training adaptations, follow
the FITT (Frequency, Intensity, Type of Exercise and Time)

Frequency may be the most important factor when combining
strength and endurance training (McCarthy et al. 1995).
Limit the frequency of same-day concurrent training to no more
than 3 days a week (Bell et al. 1991; Leveritt et al. 2003; McCarthy
et al. 1995; McCarthy, Pozniak & Agre 2002). Always consider
which mode is more important for the individual. For example,
if a client’s goal is to increase endurance for a 10K road race,
then endurance training should be performed prior to strength
training, or on alternate days, so as not to compromise results.
Most important, note that performing endurance and strength
exercises on the same day may compromise strength development
(Sale et al. 1990).

The intensity factor applies to both endurance and strength
training. According to Chtara and others (2005), a minimum
of 50% of VO2max must be attained to see cardiovascular advantages.
Additionally, an intensity of 70% of heart rate reserve
has been shown to elicit cardiovascular fitness without compromising
strength development (McCarthy et al. 1995; McCarthy,
Pozniak & Agre 2002). The recommended volume of strength
training is 3 sets of 6–8 repetitions of eight lifting exercises with
approximately 75 seconds of rest between sets and 2 minutes of
rest between each lifting exercise (McCarthy et al. 1995;
McCarthy, Pozniak & Agre 2002). For clients over the age of 50
years, 10–15 repetitions are recommended. Vary strength training
intensity and volume by weight, number of repetitions, length
of rest periods or number of sets. Perform strength training
exercises at moderate to slow speed, through full range of
motion and in a controlled manner, emphasizing both the concentric
and eccentric phases (ACSM 2000).

The type of exercise used for endurance training can be any of the individual’s favorite exercises or activities. The greatest improvements
in cardiorespiratory fitness are seen with exercise that
involves large muscle groups; for example, walking, hiking, running,
stair climbing, swimming, cycling, rowing or cross-country
skiing (ACSM 2000). The type of exercise used for strength training
might include circuit training, traditional strength training or
explosive weight training. The workout should address the entire
body; that is, the exercises should include squats, leg extensions,
hamstring curls, bench presses, lat pull-downs, biceps curls, shoulder
raises and abdominals work (Leveritt et al. 2003;McCarthy et
al. 1995;McCarthy, Pozniak & Agre 2002).

In relation to an athlete’s sport performance, design a program
that optimizes the training factors essential to the client’s
sport (Glowacki et al. 2004). (See “Concurrent Training for a
Recreational Triathlete” chart for an example). As a reminder, if
cardiovascular fitness is the client’s main objective, make sure
that, in a same-day workout, endurance training precedes
strength training. Performed first, strength training can produce
muscle fatigue, thus reducing the cardiovascular effectiveness of
endurance training (Chtara et al. 2005).

According to McCarthy and colleagues (1995), 50 minutes a
day of either strength or endurance training is sufficient to promote
both aerobic and strength development (McCarthy,
Pozniak & Agre 2002). The time, or duration, will depend on the
activity’s intensity; for example, perform moderate-intensity activity
for 30 minutes or more and high-intensity activity for
20–30 minutes. Increase duration gradually as the individual
adapts to the training stimulus without fatigue or injury (ACSM
2000). (See the charts for guidelines on concurrent training, endurance
training progression and strength training progression
for recreational exercisers.)

Concurrent Success

When working with a recreational exerciser like David, the client
introduced earlier, consider the many factors involved in developing
a concurrent training schedule. Carefully plan the proper
strength and endurance modalities. For example, in order to
maintain strength and stamina for his recreational basketball
games, David would perform 3 sets of 6 repetitions of full-body
exercises 2 times a week. In addition, he would run on a treadmill
at least once a week for 45 minutes at 70% of his maximum heart
rate. The sessions should be sequenced and timed so as not to interfere with his fitness goals. Don’t forget to factor in volume,
intensity, frequency and training status, which you will assess early
on (Chtara et al. 2005; Glowacki et al. 2004;McCarthy et al. 1995).
When these variables are appropriately accounted for, your concurrent
training program will offer the biggest overall benefit.

Kriston Koepp, MS, CSCS, is an exercise physiologist and sports performance
coach at Performance Edge Sports Training in Hayden, Idaho.
She specializes in training high-school and college athletes of all sports.

Jeffrey M. Janot, PhD, is the technical editor of IDEA Fitness Journal.
He is an assistant professor of human performance in the department
of kinesiology at the University of Wisconsin–Eau Claire.


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Kriston Koepp, MS

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