Content uploaded by Michael Hartman
Author content
All content in this area was uploaded by Michael Hartman on Mar 07, 2014
Content may be subject to copyright.
76
International Journal of Sports Physiology and Performance, 2007;2:76-86
© 2007 Human Kinetics, Inc.
Hartman, Clark, D. Bemben, and M. Bemben are with the Dept of Health and Exercise Science, Uni-
versity of Oklahoma, Norman, OK 73019. Kilgore is with the Dept of Kinesiology, Midwestern State
University, Wichita Falls, TX 76308.
Comparisons Between Twice-Daily
and Once-Daily Training Sessions
in Male Weight Lifters
Michael J. Hartman, Brandon Clark, Debra A. Bemben,
J. Lon Kilgore, and Michael G. Bemben
Context: Many elite athletes use increased daily training frequencies as a means
to increase training load without substantial published literature to support this
practice. Purpose: To compare the physiological responses to twice- and once-
daily training sessions with similar training volumes. Methods: Ten nationally
competitive male weight lifters (age 20.5 ± 1.2 y, body mass 92.9 ± 23.6 kg,
training history 5.5 ± 1.5 y) were matched on body mass and training experience,
then randomly assigned to train either once or twice daily for 3 wk. Isometric
knee-extension strength (ISO), muscle cross-sectional area, vertical-jump peak
power, resting hormone concentrations, neuromuscular activation (EMG), and
weightlifting performance were obtained before and after the experimental train-
ing period. Results: All dependent measures before the training intervention were
similar for both groups. A 2-way repeated-measures ANOVA did not reveal any
signicant main effects (group or trial) or interaction effects (group × trial) for
any of the dependent variables. There were also no signicant group differences
when parameters were expressed as percentage change, but the twice-daily training
group had a greater percentage change in ISO (+5.1% vs +3.2%), EMG (+20.3% vs
+9.1%), testosterone (+10.5% vs +6.4%), and testosterone:cortisol ratio (–10.5%
vs +1.3%) than did the once-daily training group. Conclusions: There were no
additional benets from increased daily training frequency in national-level male
weight lifters, but the increase in ISO and EMG activity for the twice-daily group
might provide some rationale for dividing training load in an attempt to reduce
the risk of overtraining.
Key Words: weight lifting, training frequency, performance
Currently, there is a paucity of information on the physiological effects of
increased daily training frequency. Anecdotal evidence suggests that there are both
physiological and performance benets associated with multiple daily training ses-
sions,1 as many high-performance athletes from the sports of bodybuilding, power
Twice-Daily Training in Weightlifters 77
lifting, and weight lifting2,3 use multiple daily training sessions to improve perfor-
mance. The underlying physiological mechanisms remain unknown, however.
During periods of high training load, many well-trained athletes divide their
training into multiple daily training sessions.2,3 Because the intensity of a workout
is inversely related to its duration, splitting workouts into 2 or more daily sessions
enables athletes to maintain high training intensity while still performing the same
volume of exercise per day. Possible benets of split training volumes might include
a more favorable anabolic environment4-6 and increased neuromuscular efciency,7
which could decrease an athlete’s risk of unplanned overreaching or overtraining.
Other authors have theorized that frequent training sessions followed by periods
of recovery might allow for greater training intensity through maximal energy
utilization and reduced fatigue during exercise.2
A potential indicator of training state relevant to resistance exercise is the
response of anabolic and catabolic hormones. The response of anabolic and catabolic
hormones, specically testosterone, cortisol, and the ratio of testosterone to cortisol
(testosterone:cortisol), could validate the effectiveness of multiple daily training
sessions. Hakkinen et al4,5,8 examined the hormonal response of twice-daily training
(TDT) in men during periods of 1 day and 1 week. They reported acute improve-
ments in T: cortisol after TDT during both a 1-day and a 1-week training period.
Although not conclusive, these data might indicate the potential benets of TDT
for creating a positive hormone balance that could potentiate muscle hypertrophy
and result in enhanced sport performance.
Additional measures of neuromuscular performance might also be potential
indicators of the training response. For example, changes in surface electromyo-
graphic (EMG) amplitude are indicative of changes in motor-unit activation and
have been associated with acute increases in maximal strength largely based on
neuromuscular improvements.9 The measurement of a maximal-effort vertical
jump10 and testing of the maximal efforts in the competition lifts in national-level
weight lifters10,11 have also routinely been used to determine athletes’ responses
and the effectiveness of high-intensity training.
The purpose of this study was to compare the physiological responses between
twice-daily training sessions and once-daily training sessions with similar train-
ing volumes in national-level weight lifters. This study examined the response of
increased daily training frequency on muscle strength and power, muscle hypertro-
phy, neuromuscular activation, and resting hormone concentrations. The information
gained in this study might expand the knowledge base of multiple daily training
sessions and help coaches program their athletes’ training.
Methods
Subjects
Subject characteristics for 10 male weight lifters are presented in Table 1. Each
weight lifter who participated in this study had competed in at least 1 national-level
event and was recruited from a USA Weightlifting Regional Development Centers
(Wichita Falls, Tex). All subjects had similar histories of physical activity and
competition, all had followed a similar training program for 6 months before the
study, and all had trained continuously for competitive weight lifting for at least 1
78 Hartman et al
year. Subjects signed an informed consent and completed a health questionnaire and
screening. Testing protocols were consistent with and approved by the University
of Oklahoma human subjects research committee (IRB# 00003191).
Experimental Design
The study protocol was designed to determine the effects of increased daily training
frequency on physiological characteristics related to maximal sport performance in
national-level weight lifters. Testing was conducted before and after a 3-week experi-
mental training period in which the daily training volume was designated as either
1 or 2 daily training sessions with similar daily training volume (see Figure 1). The
Table 1 Descriptive Measures, Mean ± SD*
Variable G I (n = 5) G II (n = 5)
Age (y) 20.2 ± 1.4 20.9 ± 0.9
Body weight (kg) 94.0 ± 29.6 91.8 ± 19.3
% Fat 18.4 ± 11.2 16.9 ± 9.1
Training (y) 4.8 ± 1.0 3.5 ± 0.4
Snatch (kg) 111.0 ± 23.1 114.0 ± 28.5
Clean and jerk (kg) 139.0 ± 39.2 136.5 ± 32.5
Squat (kg) 196.5 ± 39.2 179.5 ± 41.2
*Group 1 (G I) performed once-daily training, and group 2 (G II) performed twice-daily training.
Figure 1 — Weekly organization of daily workload between groups. All groups performed
the same workouts at the same relative intensity. Group 1 (G I) performed all of their train-
ing in a single training session (4 sessions/wk), and the training volume for group 2 (G II)
was split between twice-daily training sessions (8 sessions/wk).
Twice-Daily Training in Weightlifters 79
3-week training program was chosen for several reasons. First, in order to validate the
research design and evaluate the ndings obtained by Hakkinen et al (1993n), the
current study incorporated a similar 3-week period as their study, which evaluated
female athletes. In addition, the weight-lifting athletes in the present study typically
trained in 3-week blocks, so, in an attempt to limit any unnecessary distractions to
the athletes, the 3-week training period remained unchanged.
Training Protocol
Subjects were paired by body mass and training results and randomly divided into
2 groups. Group 1 (GI) performed all of their training in a single training session
(4 sessions/wk), and the training volume for group 2 (GII) was split between twice-
daily training sessions (8 sessions/wk) with at least 3 hours of rest between sessions.
The training load imposed during the study was a variation on published research
and training programs for competitive weight lifting proposed by researchers and
coaches.12 All subjects completed a 1-week period of reduced training load before
the 3-week experimental training periods to ensure recovery and accurate baseline
measures. All training took place under the supervision of certied coaches and
experienced sport scientists. All training loads were predetermined for the subjects
based on training results, quantied by the researchers, and kept constant for the
duration of the experiment (see Table 2).
Table 2 Experimental Training Protocol
Day Exercises
1 Squat 5 × 5 at 85%
Front squat 5 × 3 at 95%cjn
Jerk 6 × 1 at 85–90%cj
Accessory 3 × 10
2 Snatch 5 × 1 at 80–90%
Clean and jerk 5 × 1+1 at 80–90%
Snatch (blocks) 4 × 2 at 75%
Gluteal–hamstrings raise 3 × 10
3 Squat 5 × 5 at 75%
Push press 5 × 1+3 at 80%
Jerk 6 × 1 at 85–90%cj
Accessory 3 × 10
4 Snatch 5 × 1 at 80–90%
Clean 5 × 1 at 80–90%
RDLn 4 × 4 at 85%cj
Gluteal–hamstrings raise 3 × 10
80 Hartman et al
Muscle Strength
Muscle strength was determined by measuring isometric strength of the knee
extensors of the right thigh using a Biodex System 3 dynamometer (Biodex
Medical Systems, Shirley, NY). Subjects were seated in an upright position and
secured around the chest, waist, and dominant thigh. The nondominant leg and
arms were unrestrained. The right knee was positioned at the dynamometer’s axis
of rotation and secured to the dynamometer’s lever arm proximal to the ankle.
Subjects were given several warm-up trials of submaximal isometric knee exten-
sions. After 2 minutes of rest, the subjects performed 3 maximal isometric knee
extensions (ISO). Participants were asked to produce as much force as possible
for 3 seconds, and strong verbal encouragement was provided. Two minutes of
rest were allowed between ISO trials. Peak torque (in Nm) was calculated as
the highest average torque value that occurred during any 0.5-second duration
within the 3-second ISO.
Even though weight lifting is primarily a closed kinetic chain exercise, the
seated isometric knee extension was used to assess strength of the quadriceps muscle
group. This procedure is a common laboratory test of muscle strength that allows
for a tightly controlled movement that can be consistently reproduced over time
and between subjects. In addition, the quantication of the EMG signal during a
dynamic movement makes interpretation more difcult and subject to measurement
error. Finally, this design, as stated earlier, followed the protocols of Hakkinen et
al (1993n), which used the same isometric knee-extension test in conjunction with
surface EMG to isolate the quadriceps muscles. In order to evaluate a muscle- and
movement-specic task, the snatch and the clean and jerk were also used to deter-
mine possible changes in sport-specic performance.
Muscle Power
Muscle power was determined using a countermovement vertical jump. Jumps
were performed on a contact mat (Probiotics, Birmingham, Ala). Subjects were
allowed to warm up on their own (calisthenics, etc) for 2 to 3 minutes, followed
by several practice jumps. Subjects were instructed to maintain a hands-on-hips
position in order to concentrate on hip–leg power and minimize jumping-technique
differences resulting from arm swing. All subjects were instructed to maintain an
upright posture on jumping and landing to ensure valid measurements. Four trials
were performed, with instructions to obtain maximal height on each jump. Jumps
were separated by at least 45 seconds. Flight time (in milliseconds) and jump height
(in centimeters) were calculated from the contact mat. Jump height was derived
from ight time using the common formula,
Jump height (m) = 9.81 m/s2 × ight time (s)2/8.
Peak power (in watts) was estimated using the equation developed by Sayers
et al13:
Peak power (W) = [60.7 × jump height (cm)]
+ [45.3 × body mass (kg)] – 2055n
Twice-Daily Training in Weightlifters 81
Muscle Hypertrophy
Muscle hypertrophy of the rectus femoris was determined by measuring muscle
cross-sectional area using diagnostic ultrasound.14 A Fukuda Denshi model 4500
(Fuji Electric Co, Tokyo, Japan) in conjunction with a 5-MHz linear transducer
and a Mitsubishi P90 video-copy processor was used to identify the cross-sec-
tional area of the rectus femoris of the right upper thigh. Subjects were placed
in a supine position with a rolled-up towel under the popliteal fossa. A point 15
cm above the superior border of the patella, following the midline of the anterior
surface of the thigh, was identied for measurement. The transducer was placed
perpendicular to the anterior surface of the measurement site, and care was taken
that no depression of the skin surface occurred. Measurements were obtained in
triplicate and averaged.
Neuromuscular Activation
In conjunction with the ISOs, neuromuscular activation was determined via surface
EMG. Bipolar surface electrodes were placed over the longitudinal axis of the rectus
femoris muscle of the dominant limb. Electrode placement for the rectus femoris
was 50% of the distance between the inguineal crease and the superior border of
the patella. The reference electrode was placed on the lateral condyle of the knee.
Interelectrode impedance was minimized by shaving the area and cleansing with
isopropyl alcohol. All subjects maintained the same exact electrode placement
during pretest and posttest analysis. The raw EMG signals were collected and
expressed as root mean square using AcqKnowledge 6.0 software (Biopac Sys-
tems Inc, Santa Barbara, Calif). The EMG signal was preamplied (gain × 1000)
using a differential amplier (EMG MP150, Biopac Systems; bandwidth, 1 to
5000 HZ). EMG signals were band-pass ltered (fourth-order Butterworth lter)
at 10 to 500 HZ. 0.5-second epochs of the EMG signal that corresponded with the
same 0.5-second epoch used to calculate MVC torque were used to calculate EMG
amplitude and during the MVC.
Hormone Analysis
Blood samples were obtained after an 8-hour fast and 1 day of complete rest, because
it was the intent of the test to discriminate between acute and chronic changes in
total testosterone and cortisol. Blood was collected from the antecubital vein using
a 21-gauge needle tted to a Vacutainer assembly. After collection, the 7-mL blood
sample was allowed to coagulate and was then centrifuged for 15 minutes at 3000
revolutions per minute. Serum samples were then stored at –72°C until analysis.
Testosterone and cortisol were measured using in vitro 125I radioimmunoassay kits
(Diagnostic Systems Laboratories, Inc, Webster, Tex). A Riastar Gamma Counter
(Packard Instruments, Meriden, Conn) was used to detect radiolabeled testos-
terone (or cortisol) and indirectly determine unknown testosterone (or cortisol)
concentrations based on a standard curve determined from the standard samples
included in the kits. All of the assays were carried out in duplicate according to
the manufacturer’s instructions. The sensitivity of the testosterone assay was 0.08
ng/mL, and the intra-assay coefcients of variation for the upper and lower controls
82 Hartman et al
were 8.56% and 0.69%, respectively. The sensitivity of the cortisol assay was 0.5
µg/dL, and the intra-assay coefcients of variation for the upper and lower controls
were 0.96% and 15.15%, respectively. Interassay variation between the testosterone
assays was 5.96% for the lower control and 6.84% for the upper control. Interassay
variation between the cortisol assays was 2.07% for the upper control.
Weight-Lifting Performance
Initial values for each subject’s 1-repetition maximum were entered as the most
recent sanctioned ofcial competition results in the snatch, clean and jerk, and
total. These results were obtained for each subject either 23 or 24 days before they
participated in this study. The 1-day difference is a result of the fact that lifters in
the lighter weight classes (56 to 77 kg) lifted 1 day earlier than lifters in the heavier
weight classes (85 to 105+ kg). We determined that these meet results would be an
acceptable indicator of weight-lifting performance because our goal was to limit
any unnecessary distractions to the weight lifters’ training programs.
Final testing took place 3 days after the conclusion of the experimental training
in an unsanctioned weight-lifting competition. Although the posttesting session
was an unsanctioned meet, all test conditions were similar to the pretest sanctioned
competition. Certied judges were used, all testing equipment was identical (cali-
brated equipment certied by the IWF, York Barbell Co, York, Pa), and the rules of
the International Weightlifting Federation were followed. It was assumed that for
these elite athletes, motivation to perform would be similar between the 2 testing
dates, but no actual measures were taken to quantify motivation.
Statistical Analysis
All performance measures were analyzed using Statistical Package for the Social Sci-
ences (SPSS v11.5 software, SPSS Inc, Chicago, Ill). Baseline differences between
training groups were measured using an independent t test. Two-way (group × trial)
repeated-measures analyses of variance (ANOVAs) were used to determine the
effects of the experimental training protocol on the dependent variables. In addition,
percentage change from pretraining to posttraining for each subject was calculated
([post – pre/pre] × 100) for each dependent variable, and a group comparison was
made using an independent t test. Effect size and statistical power were recorded for
each analysis completed. Effect size was calculated to indicate the magnitude of each
treatment (training-program) effect,15 and statistical power provided an indication
of the probability of making a type II statistical error. Linear regression (R2) was
used to determine the shared variability between variables. Results less than P < .05
were accepted as signicant, and all data are reported as mean ± SD.
Results
The initial analyses of baseline values of the dependent variables revealed no
statistical difference (P > .05) between groups before the experimental training.
After the experimental training, both groups experienced nonsignicant increases
in countermovement vertical jump, cross-sectional area, ISO, and EMG, with no
signicant group differences (Table 3).
Twice-Daily Training in Weightlifters 83
Table 3 Comparisons Between Training Groups, Mean ± SD*
Variable Group Pre Post % Change† ES‡
Neuromuscular
measures
CMJ (cm) I 54.8 ± 12.5 56.9 ± 9.7 3.5 ± 5.7 0.15
II 58.1 ± 6.4 58.7 ± 9.2 2.9 ± 2.1 0.29
CMJ PP (W) I 5661.6 ± 1100.2 5535.6 ± 1091.7 2.3 ± 3.2 0.12
II 5631.9 ± 1050.1 5670.0 ± 1137.6 0.4 ± 2.2 0.03
CSA (cm2) I 7.9 ± 2.0 8.1 ± 1.9 3.2 ± 5.8 0.11
II 7.3 ± 2.1 7.4 ± 1.8 2.1 ± 9.3 0.04
ISO (nm) I 304.8 ± 121.9 313.5 ± 116.3 3.2 ± 10.2 0.07
II 272.3 ± 71.4 285.3 ± 73.6 5.1 ± 13.7 0.18
EMG (µV) I 0.066 ± 0.02 0.068 ± 0.01 9.1 ± 26.0 0.12
II 0.069 ± 0.03 0.076 ± 0.03 20.3 ± 45.7 0.25
Hormone
concentration
T (ng/mL) I 6.76 ± 2.31 6.79 ± 1.81 6.4 ± 27.3 0.02
II 7.26 ± 0.58 7.95 ± 1.14 10.5 ± 19.7 0.78
C (µg/mL) I 14.26 ± 8.74 16.58 ± 7.52 31.6 ± 68.9 0.29
II 16.95 ± 5.86 20.75 ± 4.69 30.4 ± 44.8 0.72
T:C I 0.67 ± 0.46 0.57 ± 0.44 1.3 ± 63.3 0.22
II 0.45 ± 0.09 0.39 ± 0.06 –10.5 ± 22.300.80
Weight-lifting
performance
snatch (kg) I 111.0 ± 23.1 112 ± 25.2 0.6 ± 2.6 0.04
II 114.0 ± 28.5 115 ± 30.3 0.5 ± 2.5 0.03
clean and jerk
(kg) I 139.0 ± 39.2 139.0 ± 30.4 0.3 ± 2.3 0.01
II 136.5 ± 32.5 138.5 ± 30.8 1.9 ± 2.3 0.06
*Group 1 (G I) performed once-daily training, and group 2 (G II) performed twice-daily training. CMJ
indicates countermovement jump height; CMJ PP, countermovement jump peak power; CSA, cross-
sectional area; ISO, isometric maximal voluntary contraction; EMG, electromyographic amplitude; T,
testosterone; C, cortisol; T:C, testosterone:cortisol ratio.
†Percentage change = [(post – pre)/pre] × 100.
‡Effect size = (post – pre)/pooled SD.
Although it was not statistically signicant (P > .05), the twice-daily train-
ing group (G II) had a greater percentage increase in muscle strength (+5.2% vs
+3.2%, respectively), neuromuscular activation (+20.3% vs +9.1%, respectively),
testosterone (+10.5% vs +6.4%, respectively), and testosterone:cortisol ratio
(–10.5% vs +1.3%, respectively) than the once-daily training group (G I). Analysis
of the percentage variance explained (R2) thatn the proportion of variation in ISO
that can be attributed to EMG activity was also greater for G II (R2 = .84 vs .62,
respectively; see Figure 2).
84 Hartman et al
Discussion
The purpose of this study was to compare the physiological responses between
twice-daily training sessions and once-daily training sessions with similar training
loads in national-level weight lifters. Our data suggest no additional benet to per-
forming twice-daily training sessions as opposed to once-daily training sessions.
Several previous research studies have shown that high-level competitive
weight lifters are capable of performing 2 training sessions on the same day with no
injuries or decrements in performance.4-8,10,16 In fact, given sufcient recovery after
TDT, an increase in performance has also been observed.7,10 Although the subjects
in this study did not experience improvements in weight-lifting performance with
TDT, it should be noted that neither did TDT result in performance decrements.
The short- and long-term responses of testosterone and cortisol to resistance
exercise have been studied extensively in competitive weight lifters.4,8,16-19 Testos-
terone levels have been shown to decrease, while cortisol levels increase, during
brief periods (1 to 8 weeks) of very intense training.4,8,15,17 To our knowledge, the
study of hormonal response to TDT have been limited to brief training interven-
tions in weight lifters during 1 day,4 2 days,8 1 week,5 and 2 weeks of training.17
This was the rst study to examine the changes in resting hormone concentrations
in 2 groups of highly trained weight lifters training either twice daily or once daily
over a 3-week period.
Although no signicant group differences were observed in resting hormone
concentrations after the experimental training, the increased response of resting
testosterone concentration might indicate that G II was in a greater positive envi-
ronment than G I (+10.5%, 7.26 ng/mL to 7.95 ng/mL vs +6.4%, 6.76 ng/mL to
6.79 ng/mL, respectively). Cortisol responses were very similar for both groups,
with approximately a 30% increase. This increase in cortisol, coupled with the
testosterone changes, resulted in a decrease in testosterone:cortisol ratio for G II
Figure 2 — The relationship between changes in muscle strength and neuromuscular
activation. Group 1 (G I) performed all of their training in a single training session (4 ses-
sions/wk), and the training volume for group 2 (G II) was split between twice-daily training
sessions (8 sessions/wk).
Twice-Daily Training in Weightlifters 85
(indicating an enhanced anabolic:catabolic ratio) compared with G I. These ndings
are similar to those of Hakkinen et al.4,5,8 In general, effect sizes were low (0.01
to 0.27), with G II cortisol (0.65), G II testosterone (1.19), and G II testosterone:
cortisol ratio (–0.67) being the exceptions. These effect sizes, coupled with our
fairly small sample size resulted in low statistical-power values for the main effects
(trial and group power values ranged between .55 and .10) and interactions (power
values ranged between .20 and .10). These power values, although not close to
the optimal value of .80, were quite comparable to previously published research
in this area.15,19
Previous research has demonstrated a possible neuromuscular benet from
dividing the same daily training load into 2 separate sessions. Hakkinen and Kal-
linen7 investigated neuromuscular adaptations in 10 female athletes during an
intensive strength-training period for 3 weeks and during a separate second 3-week
training period when the same total training load was distributed into 2 daily ses-
sions.7 The authors concluded that isometric strength, muscle cross-sectional area,
and muscle activation determined via surface EMG increased during the second,
twice-daily, training period. They suggested that twice-daily training sessions
were more conducive to muscle hypertrophy and might offer a more effective
neuromuscular training stimulus.
The ndings from the present study demonstrated a greater increase in strength
(+5.1% vs +3.2%) and muscle activation (+20.3% vs +9.1%) for the TDT group
than for the once-daily group. These results support the ndings of Hakkinen and
Kallinen,7 who reported that the division of daily training loads into 2 small ses-
sions might be more favorable for neural adaptations leading to increased strength
development rather than muscle hypertrophy,7 as well as the study by Hakkinen
and Pakarinen,8 who reported that male strength athletes performing 2 weeks of
TDT experienced signicant increases in isometric strength compared with the
same daily training load performed in once-daily sessions.8
Practical Applications
and Conclusions
Progressive overload training might be an ineffective method of increasing training
loads in well-trained athletes.3,8 Therefore, additional workouts have been proposed
as a method to increase total training load while potentially reducing the risk of
overtraining and injury.2,20 There were larger increases in countermovement verti-
cal-jump peak power, ISO, EMG, and testosterone concentrations observed for the
twice-daily training group, even though these changes were still statistically similar
to the once-daily training group. Perhaps more interesting is the enhanced benet to
the neural aspects of muscle function indicated by the increase in EMG amplitude
and the increased testosterone and testosterone:cortisol ratio for the TDT group.
Improvements by well-trained athletes are often small and limited because these
individuals are already near their physiological peak in most performance measures,
but even small improvements in performance, similar to those demonstrated in this
study, might provide some rationale for increased training frequency. By devoting
less time to a single session, athletes might be able to train at higher intensities,
which could lead to better performance, but further research is still warranted.
86 Hartman et al
References
1. Kraemer WJ, Adams K, Cafarelli E, et al. American College of Sports Medicine posi-
tion stand. progression models in resistance training for healthy adults. Med Sci Sports
Exerc. 2002;34:364-380.
2. Fleck SJ, Kraemer WJ. Designing Resistance Training Programs. 2nd ed. Champaign,
Ill: Human Kinetics; 1997.
3. Zatsiorsky V. Science and Practice of Strength Training. Champaign, Ill: Human Kinet-
ics; 1995.
4. Hakkinen K, Pakarinen A, Alen M, Kauhanen H, Komi PV. Neuromuscular and hor-
monal responses in elite athletes to two successive strength training sessions in one
day. Eur J Appl Physiol. 1988;57:133-139.
5. Hakkinen K, Pakarinen A, Alen M, Kauhanen H, Komi PV. Daily hormonal and
neuromuscular responses to intensive strength training in 1 week. Int J Sports Med.
1988;9:422-428.
6. Hakkinen K. Neuromuscular responses in male and female athletes to two successive
strength training sessions in one day. J Sports Med Phys Fitness. 1992;32:234-242.
7. Hakkinen K, Kallinen M. Distribution of strength training volume into one or two
daily sessions and neuromuscular adaptations in female athletes. Electromyogr Clin
Neurophysiol. 1994;34:117-124.
8. Hakkinen K, Pakarinen A.. Serum hormones in male strength athletes during intensive
short term strength training. Eur J Appl Physiol. 1991;63:194-199.
9. Moritani T, Devries H. Neural factors vs hypertrophy in the time course of muscle
strength gain. Am J Phys Med. 1979;58:115-130.
10. Warren BJ, Stone MH, Kearney JT, et al. Performance measures, blood lactate and
plasma ammonia as indicators of overwork in elite junior weightlifters. Int J Sports
Med. 1992;13:372-376.
11. Hakkinen K, Kauhanen H. Daily changes in neural activation, force-time and relaxation-
time characteristics in athletes during very intense training for one week. Electromyogr
Clin Neurophysiol. 1989;29:243-249.
12. Stone MH, Pierce KC, Sands WA, Stone ME. Weightlifting: program design. Strength
Cond J. 2006;28:10-17.
13. Sayers SP, Harackiewicz DV, Harman EA, Frykman PN, Rosenstein MT. Cross-valida-
tion of three jump power equations. Med Sci Sports Exerc. 1999;31:572-577.
14. Bemben MG. Use of diagnostic ultrasound for assessing muscle size. J Strength Cond
Res. 2002;16:103-108.
15. Rhea MR. Determining the magnitude of treatment effects in strength training research
through the use of effect size. J Strength Cond Res. 2004;18:918-920.
16. Busso T, Hakkinen K, Pakarinen A, et al. A systems model of training responses
and its relationship to hormonal responses in elite weightlifters. Eur J Appl Physiol.
1990;61:48-54.
17. Kraemer WJ, Fry AC, Warren BJ, et al. Acute hormonal responses in elite junior
weightlifters. Int J Sports Med. 1992;13:103-109.
18. Fry AC, Kramer WJ, Stone MH, et al. Endocrine and performance responses to high
volume training and amino acid supplementation in elite junior weightlifters. Int J
Sport Nutr. 1993;3:306-322.
19. Fry AC, Kramer WJ, Stone MH, et al. Endocrine responses to overreaching before and
after one year of weightlifting training. Can J Appl Physiol. 1994;19:400-410.
20. Stone MH, Fry AC. Increased training volume in strength/power athletes. In: Kreider
RB, Fry AC, O’Toole ML, eds. Overtraining in Sport. Champaign, Ill: Human Kinetics;
1998:87-105.
